It's a bit silly to assume that demand is the only driver. At some point, people can only buy what's supplied. If 99% of the stuff available is cheap junk and I don't have time to sort through that, likely I'll buying that cheap junk (or nothing at all).

One example is if a high quality item is no longer produced because the company or division selling it goes out of business as it's priced out of the market.

Supply-side domination/flooding can and does impact buying habits.

Oh, I'm sure its profitable, but nobody who has bought a fake charger on Amazon has demanded it. The amazing manufacturing and logistics capability is perfect for scammers.

Given that half the complaints I hear about Amazon are cheaply produced counterfeit goods sold at full price, I wouldn't be so quick to blame all of their failings on consumer demand.