If it were an ideal free market with an infinite amount of competitor, you’d be right. That logic ceases to function in a monopolistic context. In the case of YouTube it’s not “go to the competition” because there’s none. It’s “stop watching online videos”, which is still possible but a huge shift in habits, hobbies, and cultural environment. It’s extremely difficult and only a tiny minority will succeed because human’s psychology is a real thing.
It’s apparently early in development, but there’s an ActivityPub implementation of wikis made by one of Lemmy’s dev.