Yeah, every YT creator that is serious about their job should have their own website with a copy of the videos, and I find it really curious that this doesn't seem to be much of a thing? At best I'm seeing merchandise webshops. But you'd think these people would be multi-channel and have a website, youtube, all the social medias, etc, and the bigger ones a company to manage them all.
But I suspect that as they get bigger, they enter in exclusivity / no-compete contracts with Youtube, and if they detect the same video hosted elsewhere, they get taken down or something.