I’m reasonably confident that the reason has a lot to do with social proof. I don’t think it has much to do with UX, or amount of content, because both of those reasons would require people to actually try the fediverse to find out. In my experience, people don’t cite reasons as to why they won’t try a lesser-known platform, they enter a low-key fight-or-flight mode and sort of go blank, shut down, and don’t engage with the idea either way. It’s kind of spooky once you notice it in person.

To speculate, I think perhaps centralized, corporate services have an immediate advantage, because a brand name and a logo inherently provides a certain amount of social proof, since corporate brands and logos are so central to Western culture.