My primary reason for severely limiting my Amazon purchases is that I simply no longer trust them.
Almost every product search is flooded with fly-by-night random-name sellers intent on drop shipping what look to be the same identical cheapest-quality-possible products direct from China. And even if you do find a brand name there's no guarantee that it too won't be a knock-off.
This, on top of of all of the other issues mentioned is what's killed Amazon for me.
The sad part is that it really doesn't need to be that way. Costco is a very profitable company, known for its good wages and fair treatment of its workers.
Amazon could do the same, but they won't. I mean, why settle for $150 billion in profit when you could have $152 billion?