True, but you're expecting the platforms to behave honorably and not in the way that maximizes their profits. My point is the platforms' business model is a consequence of the economics of online information distribution.
Or to put it differently: anyone is free to create a competing platform that only hosts "high quality" content, but it seems no one has found out how to make that work on a large scale so far.
That's a good reason to regulate some of these practices out of existence. As you say, what happens today is a natural low point in the landscape of online information distribution; the only way to raise it is to reconfigure the landscape.
Or to put it differently: anyone is free to create a competing platform that only hosts "high quality" content, but it seems no one has found out how to make that work on a large scale so far.