The thing that "sucks" in Amazon's marketplace - is having US entrepneurs , buying some Chinese crap, doing some marketing and playing some tricks(SEO, fake reviews, etc) and over-charging on products.

In theory, with the right tools competition could sort that out.

But this theory doesn't work, not in Amazon, and not in many other online marketplaces.

So the solution is: exclusive brands, controlled by Amazon.

Amazon works hard on scaling that strategy.

And once Amazon is deeply invested in that strategy, a low-quality marketplace seems like a good thing.