On Macs, users can download and install apps freely from the internet, and that platform isnt "a morass of freemium games and ad slop".
Why is that for one platform, everything needs to go through AppStore while the other it is OK - and both are equally secure?
Are you sure you're not falling for Apple's reality distortion field?
Not OP, and not that I buy that the App Store serves its purpose given what's currently on it, but I just don't think the two platforms are comparable.
iPhones outnumber Macs something like 10:1. The user base tech literacy is lower on average. The usage habits are different.
The payoff for creating freemium and ad slop stuff on iOS is way higher.