I doubt it was because of that reader's letter -- he just seems to have missed the joke. Referring to Donner's opinion on Krabbé, when the rule in that time was "if you haven't been insulted by Donner, you are a nobody in Dutch chess", just doesn't seem serious. Nor is asking for sources for "his statement that Morphy wanted to play every other chess player at the odds of a piece", which just sounds like a good joke :-)
Probably Krabbé has just become a much better writer since then, or just a different one, and sees big flaws in the writing of that old story. He probably prefers to be known for the stuff he does still think is good.
Personally I love (the Dutch version of) "The Rider". He's well known in the Netherlands. Besides being a good author and quite a good chess player, he was also a good amateur bicycle racer.
About 6 or 8 years ago I wrote to Tim Krabbé, the owner of Chess Curiosities, to ask his permission to publish an English translation of a very short story he wrote back in 1974 called, The Strange Life and Chess Career of Pablo Murphy (originally published in the Dutch chess magazine Schaakbulletin, no. 81 - 82, 1974). Sadly, Mr. Krabbé refused my request, though in the kindest and most gentlemanly manner.
I can't reproduce the story, but briefly, it was a fantasy that quickly re-capped Morphy's life (with some inaccuracies, to be sure) and supposed that Morphy didn't die in 1884, but instead returned to chess. The story culminated in a title match between World Champion Emmanuel Lasker and 58 year old Paul Morphy in 1895. The one game given is very funny.
Overall, the story is flawed but rather charming which is why I wanted to publish an English translation of it online. However, Mr. Krabbé told me he felt the story was sub-standard, a feeling that may have been fostered by a reader of Schaakbulletin, who in the following issue had some unkind words to say about Mr. Krabbé and his story:
Coming right to the point I want to say this:
Let Mr. Krabbé stop writing horrible articles like "The Strange Life and Chess Career of Pablo Murphy". The general public already knows little or nothing about chess history, so it is absolutely unnecessary to add the rubbish as in the aforementioned article. You may understand by now that I am angry, and indeed, you are right about that.
Last Friday, a member of our chess club opened a game with 1. h3 I asked him how he had thought of this novelty. His reply was the astonishing "Don't you read Schaakbulletin? The world famous Morphy played this in 1896 against no less then Lasker."
There I was, shocked, saddened, but not silenced. I told him that this was quite impossible, because Morphy died in 1884. His cool voice filled with contempt told me that I ought to know better, because Morphy also had won the 4th prize in Hastings, 1895.
It took me quite some time and effort before I could convince our friend that he was the victim of a practical joke, that the writer Krabbé is even more paranoid than Morphy has ever been, that the largest part of the article is nonsense, that he should look up what Donner thinks about Krabbé, and that he could better spend his money on buying a book about chess history then spending it on Schaakbulletin.
I just want to question the part of the article that is somewhat in relation to the truth. Can Krabbé name the source of his statement that Morphy wanted to play every other chess player at the odds of a piece?
If I ever find a lousy article like this in Schaakbulletin, I will never read your magazine again, or no, even better, I will write a story, completely charge free, on the strange life and chess career of Mr. Krabbé.
So, what's the moral of this tale? Perhaps with a little more kindness on the part of the reader, the door to this charming story wouldn't have been shut in everyone's face now. And even 25 years after this harsh critique, we still know and admire Mr. Krabbé while the reader has faded into chess oblivion.