My last two years living in the US I spent about $3500/year at Amazon. This works out to $175/year cash back, and $105 more than my main credit card would have

My last two years living in the US I spent about $3500/year at Amazon. This works out to $175/year cash back, and $105 more than my main credit card would have yielded at 2% cash back. That was enough for me to spend a few minutes applying for and setting up the card, and I was happy with the product. You factor in the cost of the Prime membership in the break-even calculation, but as someone else noted, that does not count the value of other Prime benefits. I was already a Prime member when the store card was introduced, which means I was valuing those benefits at ~$120/yr on their own. Different people have different shopping needs/preferences. I have no trouble conceiving of the idea that what might be a good value to me might not be for someone else. In your case, I wonder how you are able to say "Sorry; that’s not a good product at all" with such conviction when there are so many people out there (~100 million) with Prime memberships in the US.