One thing I haven’t seen anyone mention directly is why Project Catalyst only lets iPad apps run on macOS, not iPhone apps: It’s because there aren’t enough good iPad apps, and Apple still wants to see people take the iPad as a platform seriously.
I mean, I understand. iPad apps should work much more cleanly on a Mac than apps designed for iPhones. That is, if your app is well-designed for the iPad, it’ll likely be a lot fewer tweaks away from being a good macOS citizen than an iPhone app. The resonance between “iPadOS”* and macOS is clear.
If you’re Apple and wanted the most Mac apps, you’d let anything from iOS run there.
But if you wanted more apps targeting Pad, you’d bribe folks by saying their iPad-specific port gets them a macOS app for free, too.
Guess which Apple did?
* The most recent Talk Show suggested that iPadOS was still just iOS by another, marketing-friendly name. I think that’s even better evidence this “iPad apps only” is a bribe, not a tech requirement.