I'm not an expert on this by any means, but just to share my opinion and limited experience, I think this tends to happen at very low and very high ratings.
Of course anyone can be a jerk, but I think those two groups tend to have more outspoken jerks because of how they view themselves.
Now when I say very low rating I don't mean beginners. Beginners, real beginners (just learning how the pieces move), understand they're new and so there's not as much ego or pride associated with the result. I mean people who have taken the first steps towards competence but aren't good enough to be humble about it. I guess this is one of the observations the dunning-kruger effect touches on.
And then at ratings much higher than mine, people can be nasty because they've had real success. Maybe they're a national champion, or have played in world class events. When their ego, understandably, gets tied into their skill, then winning and losing elicits this sort of behavior again.
I'm relatively new to this whole thing (just started playing in January), but I've noticed as my rating has improved, my opponents have become worse sports. Does this trend continue? I just started creeping up to 1100 Rapid, and I've gotten more toxic people in chat in the last few weeks than in months previous. All in a couple weeks, I've been called a name not worth repeating because I forced a queen trade (analysis showed it was the best move), repeatedly told I was going to lose (I ignore these), and accused of cheating (the guy blundered a bishop by move 14).
Since then I've disabled chat, but I've liked the good interactions I had before this trend, and I'm hoping it's just the 1100-1300 range, but I wouldn't be surprised if it happens all the time. Anybody have any insight on if it's always like this or if it's related to the current chess boom?