Because it's the only way the service can continue to exist. I don't understand where people think the money to run these things come from. It's either advertising or subscriptions. Bandwidth is not free, storage is not free the idea that you can host a service that lets literally anyone just constantly upload a continuous stream of whatever fucking dumb garbage is in their head for the day without ever asking for any kind of monetary value is the thoughts of the mentally incompetent.
It sounds like most of the features are still going to be free they're just going to offer higher quality and some other perks if you pay so that they can actually keep running the damn service