The problem is that big creators have many subscribers, because they're the only ones making videos people want to watch.
If a channel has 100 subscribers - (except if it's a brand new channel) - it's because people saw the videos and decided, no, I don't want to see this, I'm not going to subscribe.
Put all of those people on a platform together, you will just end up with a platform with more creators than viewers.
So? Why is that a problem? My wife occasionally watches this old lady who's vlogged every day for over 14 years straight. She averages 150-200 views. The people who try to build a brand end up getting outsized attention so it seems like that must be what anyone would want, but most people actually aren't trying to do that.