For Amazon retail, the the intent is not to "return what someone paid to show you" - but rather to "maximize amount of income for Amazon". I am sure they are making A/B tests with different amount of ads vs organic placement. The moment profits from placement ads displace profits from fulfillment/referral/closing fees by too much, then ads will be dialed down.
(And that's why Amazon search is so crap - yes, maybe you really want that specific part, but A-B search showed that showing random vaguely related matches will sell more stuff, perhaps because of impulse buyers, perhaps people getting wrong thing and not returning it)
And no, Grainger model is not a good fit for general shopping. Not everyone is a purchasing manager. Who wants to get no good results because they typed "picture hanging bolt" instead of "eye wood screw"?
And for AWS, bandwidth is only one of the moats. There is institutional knowledge - in existing systems, docs, people's heads, code on disk. There is common knowledge - there is ton of info on the web. The unified org/billing is huge (maybe Planetscale is so much better than RDS, but setting the relationship requires half-a-year of negotiations with finance and security, while RDS is 3 clicks away). The support is also pretty good, at least at the higher tiers.
Sorry OP, I am sure that Amazon will die one day, but not soon, and not from the problems you are describing.
Honestly, I prefer that over having to look through pages of barely-related search results to find the pearl hiding in there somewhere. But then I'm clearly not in Amazon's target market since I ditched them a few years back and was better off for it.
They can't go bust soon enough.