They use different primary mechanisms for rewarding posters with attention:
>4chan - (you)s, bumps
>Twitter - Likes, Follows
>Reddit - Likes, downvotes
There's a difference in how transitory the posts are:
>Twitter/Reddit: Highly searchable, robust archives
>4chan: Poorly searchable, scattered archives
There's a difference in moderator influence:
>Twitter/4chan: Fairly minimal and centralized moderation.
>Reddit: Basically a federation of moderated communities, with the moderators having great power to influence if they choose to exercise it.
There's a difference in allowed format:
>Reddit - 40k characters + the site even supports fucking wikis, making it a spot to post guides and FAQs and long form content.
>4chan - 2k character limit
>Twitter - 280 character limit. People tend to gravitate towards twitter during ongoing events.
Verification:
>4chan - no accounts, anonymous by default.
>Reddit - accounts
>Twitter - Blue checkmarks
Roots:
>Reddit was initially programmer/tech centric, also strongly influenced by the diggv4 migration, at this point it's very normified due to getting fucking massive. /r/jailbait, /r/atheism, death/exile of Aaron Schwartz, and charlottesville were formative moments, they're basically the root of how the site became corrupt and greedy.
>4chan was centered around nerdy sites and hobbies (somethingawful, newgrounds, weebshit, etc). "Chanology', "Fappening", "Gamersgate", and Trump2016 were other milestones. There is a long and storied tradition of "normie filters" and xenophobic rejection of outside cultural influence. It is pretty closely related to Reddit at this point as evidenced by people never shutting the fuck up about Reddit.
>Twitter was normie from the getgo and is notable for being a hive of Journos, politicos, and serious ladder climbers. Trump/pandemic caused it to become more hardline.
Basically differences in cultures have to do with differences in format and the circles the sites became popular in and history.
