[takeda]

Well, they didn't solve the chicken & egg problem, they bought the first platform that was created.

But I don't understand how large audience matters to anyone else than to the platform.

If you're just an user, there's nothing stopping you to use all of these services. In fact given the problem mentioned no one should stick to just one, because that leads to creating a monopoly.

If you're content creator, less of other creators means less competition, your videos are more likely to be featured etc.