Google pays Apple 20+ billion dollars annually to be the default search engine in Safari. I don't know whether the absence of ad blocking is a stipulation in that deal or not, but I have to imagine that if Apple blocked ads in Safari by default, that deal would not be renewed.

Apple is worth nearly $4T. I think they can afford to take a principled stand here, especially considering the current mood about big tech.

And I don't think Google would lightly give up being the default search engine on the dominant mobile platform in the USA, and significantly more dominant among upper-income users.