that said, no matter how nostalgically i tend to wax about …

that said, no matter how nostalgically i tend to wax about them, they did have their downsides:
they were often clunky and unpleasant to use. different forums had their own markdown-like syntax and shortcodes you had to learn to communicate effectively.
there was no concept of backlinks. while you could link to other forum posts, there wasn't a convenient way to see how many people had linked to a post. this might seem unimportant, but it means one of the biggest insights of the modern web (pagerank, what google was built on) can't easily be applied to forums.
forums didn't have a good way to signal importance: all posts were treated as equally (un)important, so the "good stuff" didn't necessarily rise to the top, which was further exacerbated by the next point:
they were time-based. like modern social media, older but valuable content often got drowned out in a sea of novel (but often less valuable) content.
they weren't easy to browse, keeping track of multiple conversations is tedious and time consuming