Apple added an App Store rule specifically to prohibit this, see the first FAQ at https://developer.apple.com/app-store/user-privacy-and-data-...
Tracked ads have more value because it's more likely that you'll buy something targeted at you. So you need to show less ads compared to untracked ads to extract the same value.
I think that this kind of differentiation is allowed by Apple and probably will be implemented in some apps.