While I too wish for better support for PWAs in iOS, the way push notifications are implemented in PWAs and iOS are fundamentally incompatible. iOS requires all push notifications to go through Apple's push server, which means there is only one long-poll connection to check and significant battery savings. Whereas, Google's PWA docs[1] literally lists random-push-service.com as the push server.

[1]: https://developers.google.com/web/fundamentals/push-notifica...