2. The privacy tracking controls only restrict tracking across apps and websites. Individual apps are allowed to collect data and it would be impossible for Apple to guarantee that an app couldn't collect data since they clearly can't be aware of every since implementation within the app. Notice what the terms for end-users explicitly state since a company like Meta can't get info from Apple about users across FB and Insta, for example, but may have ways to tie users together based on data they're collecting on the platform itself. Apple can't really stop that. They can only make it more difficult (which they have, as evidence by FB's reaction to the new privacy controls).
3. Where do you get the idea that they're not subject to the same restrictions? I don't see any evidence that this is the case.