The major reason social media won out is they treated themselves as a proper business that made scale plays. What forums obsessed over the user onboarding process? What forums obsessed over marketing and user acquisition? What forums were tracking user churn and how to prevent it? What forums responded to the user demand for mobile apps?

The issue is that these sites primarily were ran by people who wanted to build a community as opposed to wanting to build a forum platform. So really social media were actually competing against the forum companies and forums companies failed to modernize and failed to compete against social media ability to recommend new communities to users.