> I suspect, but don't know, that Apple doesn't know much about me and I suspect I wouldn't care about what it did.

I used to have similar thoughts. But then i realized everyone was emailing me from Gmail, sending me evites, posting pictures of events I attended but didn't RSVP to social media, etc. If you live in a moderately populated city in a western economy these apps know a ton about you. You should not give up your digital hygiene but don't lie to yourself and pretend that your friends and family are not feeding your data to the beast.