But if the reward for success is just having Amazon come in and hoover up the money you would have gotten by launching a knockoff, then suddenly there's a lot less incentive to invest in novel products. That's true both for categories where Amazon is competing and ones where it isn't currently.
I wouldn't be surprised if Amazon's replacement product is sometimes modestly worse, because a) they don't have the kind of deep expertise in a product that the original creators do, and b) it doesn't have to be as good to get the money.
And then there's after-sale support. Amazon's customer support is atrocious. The one thing they're good at is taking things back. But anything more complex and it's a nightmare.