My theory is that many people are "proud" to have bought something, either for its novelty or because they managed to get the whatever for a lowish price/discount, or - on the opposite - because they already spent an awful amount of money so it must be exceptional, or because they read somewhere that the thing is exceptionally good.
Short of the thing completely not working, they are (in good faith) convinced that they got the best and talk endlessly on how good it is, and how nothing else is as good.
Once upon a time it was typical of many self-appointed Hi-Fi experts but in more recent years I have seen the same behaviour in many other cases, from vacuum cleaners to Tv's.
I got invited to join one of these groups from a friend and got tons of free products on Amazon this way. I remember getting a free home security system that was like $500 or $600. I never even took it out of the box, just re-sold it on Facebook Marketplace.
Eventually I left the group because I felt bad leaving these good reviews when some of the products were absolutely garbage. It's an unfortunate situation for the sellers though too; people don't buy products on Amazon that don't have reviews. So if a seller can't bootstrap a few good reviews early on then they won't ever start making real sales.