Because, like all places on the internet(and places in general), it has its share of good and bad people. Chess.com doesn't test people's kindness when they sign up. You won't see any place where there aren't bad apples.
Mean


Because you can be mean on chess.com and not have to worry about getting your bell rung by the person hidden safely on the other side of the computer screen. When you take away accountability, as in having to say it face to face and run the risk of a broken jaw, then inhibition goes to the wind and the keys start tap-tap-tapping! Suddenly the kid getting constantly bullied in real life at school can become the bully online, all from the safety of that buffer zone that anonymity and many, many miles of separation from the other person offers you.
Amazing how polite people are to me in person...
Just remember, chances are the person on the other end hurling insults and quick-witted derisive comments might very well look like this:
Most people willing to say the same things to you face to face will look A LOT different, because they will be prepared to physically back up their comments before they open their mouth... unless they're just really, really dumb...
It also doesn't really help that you can't show body language and make gestures, which would typically reveal if somebody is actually being aggressive.

Wouldn't it be great if the site required webcams... Imagine how badly that snarky comment Member123 just made would go over if you couldn't stop laughing on camera at how Member123 appears to be only 12 years old... He'd get into a tissy and leave!
Wouldn't it be great if the site required webcams... Imagine how badly that snarky comment Member123 just made would go over if you couldn't stop laughing on camera at how Member123 appears to be only 12 years old... He'd get into a tissy and leave!

Wouldn't it be great if the site required webcams... Imagine how badly that snarky comment Member123 just made would go over if you couldn't stop laughing on camera at how Member123 appears to be only 12 years old... He'd get into a tissy and leave!
It totally would not be great if the site required webcams; that would be an invasion of privacy, which we Americans tend to abominate.
You missed my point. It's hard to talk tough to someone on the other end of a computer screen if you can clearly see they are a child and you are an adult, and you're laughing as they try to troll you. Of course it's an absurd idea, and was never meant to be taken seriously - Trolls would go extinct, and where would the side entertainment go?
why do people be mean on chess.com?