Because we took the set of internet users, and sorted everyone who wants to be intentionally offensive into 4chan. Which means there's not only a high density of people who like being intentionally offensive there, but that being intentionally offensive is socially rewarded, so over time 4chan users grow to want to be more and more intentionally offensive.
I think because you can't be anywhere else on the Internet anymore. It's like the system's pressure relief valve. A blaring steam whistle that's only getting worse and worse the more the Internet squeezes elsewhere.
Because the bump system combined with the finite number of threads incentivizes threads that get the highest number of replies per second. And the best way to increase replies per second is to start an internet fight.
And there is no voting, so the only possible gratification for posting is receiving a reply.
Because it's really the onlY place left to go if you want to be offensive. First forums, then platforms censored offensive people out of their niche places. Even Cloudflare participates. 4chan remains the only privately owned large forum.
Cloudflare has famously dropped websites which it deemed too controversial
It keeps people out that are unable to separate the internet from real life.
There's a lot of interesting stuff on there but I can't use the forum because I'm black and they're very earnest about telling me how subhuman I am even when it doesn't make any contextual sense to do so.
because it is effective in keeping a certain type of people out
People like me? (I'm black)
The same reason Penicillium molds produce β-lactam antibiotics. There doesn't have to be an intelligent reason, just a survival trick.