From there, you also ensure that you have a backup of all your videos. I've talked to people that only had their stuff on YouTube/Facebook/whatever. It is super risky. If you have a backup, and YouTube bans you, you can rehost elsewhere, it won't be as big, but you might still have a business afterwards.
When you're making commerce in someone's fief, they will demand tribute as well. In the confines of your own kingdom, all the ad dollars are yours.
Which also means you don't need to chase the same amounts of people to make similar coin, especially if the deals you make with advertisers are between you and the advertiser (not you, the advertiser, and the king of some other fief).
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.