The problem is that there's a ton of value created by the information the services collect. Delivering more value to advertisers allows more video creators to make their livings.
If you started your own site there's absolutely no way you could be profitable competing on both hosting costs and payout to creators.
I broadly agree that creators hugely benefit from these platforms, but that really doesn't seem to be what they're optimizing on imho. And you basically admitted they're a monopoly with that final statement.
It costs money to host video. The volume of advertising you sell supports your costs, with a fraction going to the content creators. Using information you gather increases how much advertising you can sell. The more advertising you sell the more money everyone gets.
Having a low cost infrastructure for video streaming and good advertising deals is not a monopoly, it's an investment.
If you started your own site there's absolutely no way you could be profitable competing on both hosting costs and payout to creators.