If you only host known-quality product, then the scope of what you sell is greatly reduced. This isn't because you're filtering out bad product, but because you

If you only host known-quality product, then the scope of what you sell is greatly reduced. This isn't because you're filtering out bad product, but because you do not have the resources to actually vet everything flowing through your store. And this isn't so much an Amazon thing, or restricted to particular verticals. Steam used to work this way, and they were a massive bottleneck for people who wanted to sell indie games on PC simply because they were being swamped with unsolicited content submissions. They lost out on Minecraft because of this. That's why they tried having users do their content vetting for them (see Steam Greenlight), which itself was a disaster but in a different way. Now it's just an app store: you register with Steam Direct and pay a filing fee and you can be on Steam. This is the only model that actually scales. This is the dilemma every platform holder eventually hits: it's far more lucrative to just open yourself up to all comers and ban abusive sellers than to validate that someone is above-board before selling their stuff. The latter involves losing out on business opportunities. Traditional publishing models have to vet the content they sell because it's their money they're risking on what is effectively an investment into a copyrighted work. And they lose out on a lot of opportunities. However, platforms don't need to do this: the risks they take are far lower, so it makes far less sense to review content in advance. Remember: Amazon's business model was built on the "long tail" - making any sort of subjective quality judgment contrary to the spirit of the company. And the judgment is subjective. There's very few instances where you can say a product is objectively terrible, and those are better covered by making them illegal and making platforms liable for selling such product.