People aren't really keen on taking few hours of their day to repackage and ship back something that is 20-50$.
I often buy things from amazon-like storefronts here in asia and sometimes they refund no questions asked but sometimes they require you to ship it back and 90% of the time it's not worth it. All of these "free returns" policies sound much better than they actually are.
One of more recent anecdotes:
I bought a new keyboard for my Thinkpad which said "genuine" and serial numbers in decription match ones with Lenovo's. The keyboard turned out to be fine but had no backlight. My point is that packing it up and sending it back to neihbouring country is just not worth it. I clicked refund and left a negative review and that's pretty much as far as I'm willing to go for 60$ that I've spent.
There are lots of problems with that approach, unfortunately:
Returning means you need to repack and re-ship the item. Sometimes they cover the shipping cost but not always
Sometimes the counterfeit item only becomes evident after the return window has expired, like buying a wireless adapter for game controllers that breaks in 2 months. (It turns out one of the earliest rampant counterfeit issues on Amazon was people selling knockoff USB adapters for XBox controllers, oddly enough). At that point you can't return, all you can do is leave a nasty review for the product you bought From Amazon.
Some counterfeits are basically indistinguishable from the real product unless you're an expert. If you buy some vitamins or Tylenol off amazon, do you really have the resources and expertise to identify whether they're fakes or tainted or a batch that failed to pass quality control? So now you have to convince Amazon to take this thing back.
In the end at this point Amazon knows very well how much counterfeiting is happening on their platform and they aren't taking enough effort to stop it. It can't all lie on the individual customer to spot and combat counterfeits, they aren't able to do it.
Anecdotal but I learned that some DJI drone props I bought were counterfeit about 7 months after buying them and after many drone crashes. I explained the issue to Amazon and after a couple of questions, they gave me a full refund. It was only 15$ and probably not even worth my time but it never hurts to ask.
