I used to have a large portfolio of forums in the early to mid 2000s. Reddit was really a big dagger since each sub is essentially mini forums.
That said, quality niche forums are still alive and kicking. I run one on my alma mater's sports teams that's been online since 2007.
Should also note that forums got absolutely destroyed by modern SEO changes implemented by search engines. Organic search traffic really got destroyed over the last 5 years or so.
the lack of bridging between things has been what killed the little ones, that's part of why nostr's inherent leaky design and self sovereign identity are so valuable as a way to bridge people back to a more free form internet without centralized gatekeepers pretending to moderate but actually manipulating
