There are a couple of reasons I feel okay on MS but less about Apple.
First, my desire to break up large tech companies is very correlated to their adware/spyware business model. Apple has taken a strong stance against, MS has been moving in that direction. Second, MS has multiple disparate product lines (XBox, Azure, Windows, Office, Bing/Outlook) whereas Apple doesn't really. I'm not even sure how you can divide up Apple in a meaningful way. Third, Apple currently is the only thing keeping Chrome from eating the entire web. Even MS gave up on their own browser and reskinned Chrome. Apple also is pushing a more privacy focused single login to eat at Google/FB. In my view, breaking up Apple would only make sense once we knew we had properly broken up Google/FB as right now Apple is far better at reigning in their excesses than any other entity, including the world's governments.
I agree that currently the introduction of most people to computing is a smartphone, but I don't see how breaking up Apple can make people's lives better. Until we have better ways of protecting people's privacy on an app-by-app basis, I'm happy with using Apple software on my phone.
All that said, I really would just like privacy protections, with hefty fines that enforce compliance. It seems easy enough to do, but there seems to be no stomach for it.