Except Hey, which would need the Push API to build a reasonable PWA experience. Android and Safari desktop have it, but not iOS.

https://caniuse.com/#feat=push-api

Android has this feature for how many years now?

I tried to look it up, I saw 13 years but that sounded like too long.

And they only work as websites as long as Apple's Safari engine continues to let them.

Did you know you can't ship a custom browser engine on iOS? Yup, another one of the rules. See why?

Consider the user experience of an email app that only works when you have a network connection — so you can’t even see your mail when you’re offline. Pretty lousy.

You can have offline web apps. Although apple is actively sabotaging PWA standards.