Moderation and intent are big parts of the difference too.

I don’t use 4chan but I gather that it’s a wild little corner of the internet where you can put whatever crazy shit you wish on a website that others will read, knowing what they signed up for. Basically anything goes so you get all types. You might even call it free speech absolutism.

But Twitter is actively moderated and algorithm tuned to favor a certain flavor of bias and, especially given the players involved, propaganda.

One is neutrality even in the face of humanity’s worst, and the other is actively siding with and promoting humanity’s worst.