Would you really trust Amazon enough to take that risk?
There would need to be an massively good reason to do that, and "incrementally better analytics" isn't it.
This is why it comes down to trusting Amazon. Essentially the question is "Do you trust Amazon not to do something that would be 'professional suicide', like accessing a rival company's AWS data, enough to risk giving them your data?" If you're running an online retailer that's a competitor to Amazon you should probably fall on the side of caution because companies do stupid shit all the time.
- Amazon predatory pricing
- Amazon trying to mistreat their workers (including AWS) as much as they can
- Amazon/AWS copying products, FOSS software, and messing up with companies that they invest into.
- Their complicity with all the scams going on their store.
- And a big, big etc
But, but, Amazon is not AWS! Amazon is retail and is a different environment! Yes, but it is under the same people.
Doing that at scale doesn't make them more trustworthy. Or it shouldn't. Then again I guess if you're a super-creepy stalker at large enough scale then you're Facebook or Google and instead of getting probation and a restraining order you get billions of dollars, so maybe it does work that way.