Probably because no-one was taking the bait, which is why I was disappointed when someone else resurrected it.
Why only 3 black grandmasters, none of which are American?

Uh-oh, time to slip into some sandals!
With socks too, I'll wager. Degenerate.

Folks... there are more than three Black GMs (as of 2019), but why it makes no sense to count them, name them, or debate over it. What's the point? Besides, the article people are citing is from 2010!
Some of the reasons for not pursuing chess vigorously (GM title) is a matter of "opportunity cost." It's difficult to justify spending the the long hours to pursue a GM title if you are typically occupied with making ends meet. If people here are not aware, Blacks in this country are still in the lower rungs of the socioeconomic ladder and chess is not a lucrative profession. In fact, it gives little financial return for the money spent. It is essentially an amateur activity we have for leisure... like most of us. Only a few can aspire to earn the GM title, and only a few do.
If you're studying at such a level to become a GM, you have a conundrum. How will spend your time... studying the Najdorf for four hours or finding a profession that pays so you can sustain yourself in a competitive environment? Even for GMs, chess in American does not provide any consistency. It may be painful, but it is what it is.
If you pursue a GM title, you'd better have a sponsor or you'll starve trying. One of the Black GMs made mention of his foray as a professional chess player. He topped out at about $30,000 one year. With such a competitive environment and small prize opportunities, the cost-benefit doesn't make sense. Ironically, the Black GMs have all been in more supportive environments than Maurice Ashley, who got his chess education in the U.S. (100%). He took a hard road and struggled.
The other option to make GM is to start early, get home-schooled and earn the title while you're a scholastic player. That's what the kids are doing today. The pursuit of chess excellence is so much different than 30-40 years ago. The problem is more complicated that we imagine.
Bear in mind there was a period in American chess where few home-grown GMs were produced. This coincided with the wave of emigration of Soviets and more sharks competing for paltry prize funds. The chess infrastructure is not the best and it we are talking about a country where there are few norm opportunities. You typically have to travel overseas. It's cost-prohibitive... and what are you doing? Getting a GM title? Unless you have some financial backing or inherit some funds, it's going to be difficult in a country like the U.S. This country has yet to professionalize chess and if not for Rex Sinquefield, it would be much worse than it is for chess professionals. Not the mention the attrition rate for scholastic players is awful. Chess is used as a stepping stone more than anything else.
It's not a numbers things as some argue for women, but it is also a matter of preference of how you want to spend your time. Why are there few top Black players in darts, curling, shogi, go, jockeying, yachting? Figure it out. African-Americans were not traditionally exposed to chess in the household and there were many other social alternatives in which we excelled. Chess? I learned from an encyclopedia after seeing two friends play in the neighborhood.
Fortunately for me, I went to a high school with 4,000 students and 100 players in the chess club. However, I'm the only one from the team still playing from the all-Black high school. I had some moderate success as a junior player and got up to 2150 USCF, but then I sought academics and now I'm a professor. I get to invest in chess now, but my days of chess aspirations are long gone. People make choices and if they are not tied to economic upward mobility, then they chose other options. It's not so hard to understand. Many Blacks do not become GMs in chess, but excel in other areas. One Black GM told me recently, "Chess will take your far... just not in chess."
I wrote this piece a few months ago. Enjoy!
https://www.thechessdrum.net/blog/2019/03/20/former-african-american-standouts-reap-benefits-of-chess/
I can explain because I also come from a macho culture, it's more masculine to be a boxer or a rugby player whilst being a male netball, badminton or chess player entails feminine traits.

There's a very simple explanation. There is simply just too much inherent racial tension every time someone asks a black chess player, "would you like to be white or black?. To avoid this tension, they simply don't play chess. Imagine if they 'choose' to be black and get beaten by a white guy with the white pieces. Years of racial equality get flushed down the toilet. Did Martin Luther King play chess? No. And he had 'king' in his name! Coincidence? I think not.
Its a good question. I believe in the future there will be more black GMs, I play many talented black players and some them are very strong masters. I was very fortunate to play blitz with FM Steve Booth, the lie is there is no chess culture among the black community and there is rich chess culture among blacks. Go to any park, chess club or coffee house and there is talented black players.

Which is what Chessdrummer basically was saying.
There's no coincidence that the more affluent societies of the world tend to produce far fewer chess grandmasters. It's not only a question of chess culture having been greatly stimulated in places like the former communist countries. In many of them, a university degree is still no guarantee for a good, comfortable job, whereas in countries like the United Kingdom, the US, the Nordic countries etc. (where until very recently a university degree was a virtual guarantee for a good, long and generally profitable career) chess is mostly seen as merely a pastime, and very often promoted as "capable of boosting school kids' academic performance" as its main (and often its only) USP. Personally, I can't think of a worse way of making the case for any type of game or sport. It's like saying that it's good for kids to play football, ice-hockey, etc because it'll be good for their physical stamina. It wouldn't exactly be seen as a ringing endorsement ... and I've heard numerous chess coaches say that parents have actually not wanted the kids to become too good at chess, because it would just distract them from proper schoolwork. Also, another facet of this in those above-mentioned more affluent countries is that CV-building has become exceedingly important (so that people with money have their children do various things - voluntary/charitable work, for instance - just to boost their CV with a view to land that fabulous first job years down the line), and chess to anyone uninitiated still has an exceedingly brainy image, which means that 'having represented country X at youth level in chess' looks fantastic on a person's CV. Back in the day, it used to be that players had to qualify for the World and continental youth championships, meaning that a) it was extremely difficult to qualify, and b) that only a handful from each country actually participated. Now those youth championships are thrown completely open, so anyone can compete (sometimes as long as it's done at their own expense) and 'represent their country at youth level', meaning that often many tens of players from any one country compete in each category. The fact that they were complete also-rans obviously won't show on the CV, and once they've done this a couple of times or so, that part of the CV-building exercize is done, and they can move on to the next part of the project.
It's a basic point I made.
The topic's intent, the very nature of it's title, is meant to create disparity, disharmony or discord. Pick either or others, there is nothing good to come of any discussion of such differences for people's who play chess.
Age, culture, race, religion, politics, gender, etc. .. it's all the same when any OP creates such titles. The intent is to create a negative atmosphere, one of argument and differences. Chess brings diverse peoples together, not the other way around.
I understand why "politics and religion" is taboo. But race and gender are allowed??? IMO, any topic that promotes disharmony within the chess community needs blocking.
Actually, I've started locking any new thread on the gender issue for exactly that reason.
I haven't personally seen the same frequency of this type of thread, but I am watching it.
David, moderator