It's misleading to claim that Apple has "let and helped Facebook, TikTok, Tinder etc. track users [...]" using the keychain API. The persistence you're talking about, which those companies exploit, is a side effect of how the API works, not an intentional surveillance feature. Furthermore, it's not some special API that those big companies made a deal with Apple to get access to – any iOS dev can use it.

It's a real flaw that they should've fixed a long time ago, but your conspiratorial framing makes it seem like Apple colluded with Facebook et al. to end run their own privacy protections, while ignoring the fact that Apple's App Tracking Transparency feature has cost Facebook billions.