(b) The situations you're describing hasn't really changed since Facebook added ads, so they could've had that "realization" much earlier.
(c) Apple is positioning itself as a privacy-focused company with (for example) their lawsuit regarding iPhone unlocking and their implementation of differential privacy for their machine learning algorithms. It'd be stupid to give that up and risk a triple-digit-billion-business (iPhone) for what's bound to be a small fraction of that (ads in the App Store).