ATT: Apple's App Tracking Transparency, not AT&T
FBA: Fulfillment by Amazon, not related to FB
DTC: Direct To Consumer, not Depository Trust Company
Sorry, couldn't resist :)
"boo hoo, I can't invade my users privacy anymore! Waaaaah! It's unfair"
But also, Amazon doesn’t rely on product recommendations in the first place. When I want to purchase something, I usually go to amazon.com and type in exactly what I’m looking for. No need for Amazon to guess. Amazon does make recommendations, but at least in my case they represent a tiny fraction of purchases.
In that way I’m voluntarily contributing to Amazon’s monopoly. I feel bad about that. But I use Amazon anyway because there are no alternatives that offer even a remotely comparable buyer experience.
Also, Apple didn’t limit their own advertisers from measuring conversions. So if you click an ad in Apple News and then buy an app from the App Store they will measure and charge the advertiser for that conversion without ever popping up a scary message saying Apple wants to track you. Go figure.
The companies have worked around these issues by doing stuff like statistical modeling to guess the conversion rate, but this has obvious downsides and makes everything harder, which puts them at a competitive disadvantage vs. vertically-integrated players like Apple and Amazon.
In fact they explicitly prohibit using in-app purchases for physical goods, presumably because they don’t want to deal with the headache that comes with providing customer support for those transactions.