When you go to a listing (SKU) on Amazon, it shows you a bunch of "sellers" with various prices. These sellers usually fulfill with Amazon (hence, Prime shipping). Each seller sends its merchandise to Amazon's warehouse for fulfillment (shipping to you). Amazon commingles the inventory; all of that SKU goes into one bin, no matter who provided it.
Suppose the sellers are Creator, Honest Retailer #1, Honest Retailer #2, and Sketchy Knockoff. You care about quality, so you pay extra to order from one of the three trustworthy sellers. You still have a 1/4 chance of getting one of the Sketchy Knockoff's counterfeits, because they're all picked from the same bucket.
This also explains why you might see a review stating that someone received a counterfeit, even though they ordered from the creator.