When I used Android, I just didn’t install things unless I really, really wanted them, and they were popular enough that I figured security researchers would likely be looking at them closely. (Which, of course, was a great incentive to keep using Google’s ecosystem for everything.)
I tried iOS a few years ago, and one of the big differences is that I’m a lot more confident about trying random apps; I know there’ll still be shady apps, but Apple’s vetting and the iOS security model give me a lot more confidence. I’ve installed (and paid for) a lot more apps as a result; my phone’s much more usable to me.
Somehow we're not discussing prohibiting filesystem access for personal computers? Why is this an issue for smartphones, a.k.a. a pocket-sized personal computer?
If Windows had proper filesystem sandboxing enforced on applications, ransomware would disappear overnight
And we've seen that apps that are trustworthy can be bought and sold, sometimes by companies that are very untrustworthy.