>Have any sources on that? Sellers are suspended quite often.

Sources that Amazon has gotten worse in this area over time? Sure. My own experiences, experiences of others that you can read here and elsewhere. Plenty of news stories from reputable sources (https://www.google.com/search?q=amazon+counterfeit+problems&...)

All anecdotal, of course, because only Amazon really knows the numbers, and they aren't sharing. Fair enough to say I'm guessing as to why. I don't find it unreasonable to question their practices though. It's a big enough issue that people are noticing.