Facebook and Amazon can both track you individually and correlate accounts because you need an account under your real name to use the service. They can just choose to share this information with each other. This only prevents services from using IDFA to correlate pseudonymous accounts or across services that don't require accounts at all.
I especially don't understand the complaint from Facebook with reference to the four plus apps they have where users may very well just use the same account. As it stands, they've been wildly inconsistent about this. Here is Mark Zuckerberg only six weeks ago claiming this change would be good for Facebook: https://arstechnica.com/gadgets/2021/03/as-apple-app-trackin...
I especially don't understand the complaint from Facebook with reference to the four plus apps they have where users may very well just use the same account. As it stands, they've been wildly inconsistent about this. Here is Mark Zuckerberg only six weeks ago claiming this change would be good for Facebook: https://arstechnica.com/gadgets/2021/03/as-apple-app-trackin...