I think the main bottleneck is not the installation by the vendors, but the apps available.
I believe, what is missing is an abstraction layer between the apps and the OS. If it was possible to create apps for Android and Apple in a generic way and, it was easy to add a third OS, so all the apps could be made available to the new system, a new OS would be not so limited. I know, I know, that is itself a very difficult endeavor.
The thing holding them back is apples deliberate crippling of them to make them hard to install, slow, buggy, and not having basic platform features.
I believe Apple is deliberately doing that because if they supported PWA's properly, they'd loose all vendor lock in.
imo pwa's on webkit are only crippled in regards to the google extensions that make no sense for most usecases but ad-tracking.
Classic example: Oil companies "investing" in clean tech in the 90's, sucking up government grants and public attention and never really getting anywhere probably slowed down the switch to renewables by 10+ years.