There are plenty of ways you could do that. Off the top of my head: Every video-posting account must be validated with, e.g., a credit card. New accounts have clear posting limits. Accounts behaving badly get charged for cleanup. If you want to get paid by YouTube you have to go through an extensive validation process, including background check. If you are found to be abusing the platform, money will be clawed back, and if you can't prove sufficient resources to handle a clawback, you instead have to post a bond or find an insurer who will guarantee you.
Sure, some videos may go to another platform. And for most things, that'd be fine. A lot of videos people post on YouTube are just accidentally hosted there, and would be just as good posted on, e.g., Facebook, Twitter, or another personal account provider. But there's a whole class of garbage that YouTube has because one way or another it allows people to get paid. That garbage is a negative externality on the rest of us, and there's no particular reason for us to allow YouTube to profit from it.
Sure, some videos may go to another platform. And for most things, that'd be fine. A lot of videos people post on YouTube are just accidentally hosted there, and would be just as good posted on, e.g., Facebook, Twitter, or another personal account provider. But there's a whole class of garbage that YouTube has because one way or another it allows people to get paid. That garbage is a negative externality on the rest of us, and there's no particular reason for us to allow YouTube to profit from it.