They are that rare. The problem is that with multiple millions of players, there are enough DMs that if even 1 in 100 were like that, it would still be a significant number of DMs for the internet to complain about. And humans go to the internet to complain many, many more times as often as they go to say how good someone or something was.
You're just seeing a lot of it posted, which is deceptive in that it makes it incorrectly seem like it happens left, right and center. It's like Teslas. People are all like, "I would never drive a Tesla, because they catch fire and kill you." The news has sensationalized Tesla car fires and it seems like it happens all the time. The truth is that Tesla car fires are much more rare than gasoline vehicle fires, and nobody talks about how they won't drive a gas vehicle because they catch fire and kill you. That's because even gas vehicle fires are pretty rare. Gas vehicle fires don't get the ratings like Tesla fires do, so they aren't all over the news.