However, let's not ignore the massive market for apps supported by ads. iOS developers had a way to be modestly compensated (without the Apple tax) in return for an app that is available to anyone for free. How much less profitable are ads going to be because people can opt-out of IDFA? I don't know. But I'm sure many developers are going to think twice about developing free apps for iOS.
Conspicuously, Apple also just reduced it's commission from 30% to 15% overnight for these developers. It seems to me like Apple really wants to nudge developers into creating paid apps. Is it because of privacy, or because it's better for Apple's bottom line? Probably both.
I'm glad Apple found a way to monetize privacy, but I didn't mind installing a free app with a few ads if I knew that I'd only use it a few times.