4chan doesn’t rely on likes or upvotes, and posts are ostensibly "anonymous" (not attached to a persistent identity). Instead, users earn their feel-good chemicals by the amount of attention they can generate, positive or negative, as measured in number of replies or impact on board culture. Threads themselves are kept alive based on how often they receive a reply relative to their peers, with each board having a set capacity for active threads; the least popular threads are quickly pruned out of existence.

This system encourages gamifying replies by creating content that elicits strong fear, anger, or excitement responses, or opinions or media so shocking that it’s impossible not to interact with them. Combined with a lax free-speech policy, you get a website that reinforces the nastiest, most unsanitized content, often far-removed from reality, which can exacerbate mental illness or depression among vulnerable populations.

While other social media platforms also encourage their creators to exploit fear, anger, or excitement, leaning too heavily on emotionality without being acceptable to your audience can cause your post to be buried or underperform. Emotional engagement is only one factor in success, alongside the like-to-dislike ratio, watch time, creator reputation, and palatability to advertisers. If you post, e.g., an emotionally provocative YouTube video that completely dismantles your audience’s preexisting conception of you (a leftist posting a right-wing video), the video will likely be dislike-bombed and thus unable to climb very far in the algorithm, while your reputation will be tarnished among your hardcore fans. Even on a more pseudo-anonymous platform like Reddit, going too far against the grain of a subreddit will get your post downvoted and hidden from anyone not sorting by new, and probably deleted by the mods.

4chan doesn’t have these issues. Even if you are outside the Overton window of a specific board, as long as the post has enough substance to fuel outrage (there is a difference between cheap outrage and more visceral, long-lasting outrage that can only be created by someone intimately familiar with the subject), your post can still be successful, although you will be bombarded with racial slurs and death threats. It’s ragebait in its purest form.

Disclaimer: I have never posted on 4chan and these are just my observations from lurking.