Social media won because it's better for the consumer and producer.

For the producer, it's free infrastructure but it's also advertising. Having a large subreddit means your game getting recommended to others and potentially being seen being introduced to more people.

For the consumer, these social media sites do usually do provide a better experience in showing people what they want to see and keeping away stuff they don't.

I'm sympathetic to forums just because I think if someone likes something they shouldn't need to join a potentially social media site with potentially toxic designs and sub-communities. But these are negative internalities that people mostly ignore.