I think you mean by design. Ads above search results can be tracked because they're shown within the App Store, so they don't require looking at "who is this user" from within the downloaded app, they can just differentiate based on where it was placed, like Google Ads. The only case I can see here is "why does apple get to be the only ones with ads on search results" but then you're arguing the same point you'd use against Google, so it all comes down to what the potential Google antitrust lawsuit says and if the DOJ cares about this enough to later file suit against Apple.