Apple's Appstore rules forbid push-notification for marketing/advertising, and I get way less useless notifications by default on iOS. On Android, I often get notifications from major Appmakers in the sort of "We haven't seen you for a while, checkout what you miss in our App!" or "There is a competition in our App, take part and win a free XXX). Yes, you can disable notifications as a whole for an App, but that would also disable those notification that I want to receive and are essential.
If you would allow PWAs installed from outside the Appstore to send push-notifications, major 3rd party app makers would abuse that as means to "increase engagement" (their marketing lingo for spam) with their users.
The AppStore review operates on a spirit-of-the-law basis, instead of the letter-of-the-law.
There's no such thing as PWA or PWA support. It's several dozen different standards of varying quality and usefulness. And people randomly chose arbitrary selections of those standards and claim that this selection is a true PWA support.
Thank god Safari doesn't allow notifications and it should continue not allowing them.