Probably because they’re making plenty of money from their existing relationships with carriers. There’s no reason for Apple to vertically integrate when they’re already the dominant player in their carrier relationships.
Google relies heavily on advertising revenue so needs to interject any time there's a threat to that. Doesn't matter if it's a web browser that defaults to bing or an ISP that interjects their own ads.
On the other hand, Apple relies heavily on hardware sales for revenue.
On the other hand, Apple relies heavily on hardware sales for revenue.