How did vBulletin/phpBB came to dominate the forum space in the English internet? To me, that seem like the source of a lot of problems for the forum culture and centralization into Reddit.
The thing that got vBulletin to succeed over UBB was themes and customizations/hooks.
The thing that made phpBB popular was it didn’t require a license like vBulletin.
Honorable mention is SMF. It replaced YaBB SE, was also free, but had an amazing mod system that didn’t require any manual file editing. And [Unknown] and his team did a great job on the database keeping it way more performant than phpBB was in the free space.