Even if the platform weren't originally a microblogging one, longform text is basically over at a societal level because the majority of internet users now are on phones, and that medium discourages longform text. You can see this from Reddit, where comments a decade ago where often much longer, a couple of solid paragraphs, and now they tend to be microblogging-length inane quips.

It depends on which subreddit you're on. Reddit has this strange dynamic where it's simultaneously a series of web forums, and a single feed scrolling app. Some subs have more of a community feel and they can encourage longer form posts depending on the subject matter.

What's really notable is how the tone of a small subreddit post changes completely if a post gets boosted to everyone's front page. There's a small cycling sub I read with good posts about routes, tips, and advice. When something reaches the front page, it becomes a shitshow of car v bike culture war bullshit.