What's the difference with Safari? (not a JS dev, so this is not familiar territory)
Apple has a vested interest in pushing users towards their walled garden for apps, while Google and Mozilla are trying to bring app-like experiences to the browser. There are hints of Safari supporting serviceworkers but I'm not holding my breath.
Highly recommend Alex Russel's talk on progressive web apps as background: https://m.youtube.com/watch?v=x7cfLDFVyHo
I happen to agree that offline-readiness (via service workers) is at the core of whether the open web will continue to be a relevant medium.
And desktop users of Chrome, Firefox, and soon Edge (which has support implemented behind a flag).
Laptops and desktops still benefit, but less so because generally if you sit down to use one of those devices in an area of poor connectivity, you're going to run out of things you can do with your serviceworker's cached content pretty quickly. If you're developing a serviceworker, the improved experience will be most felt by mobile users.
https://github.com/gdnmobilelab/hybrid
If you have an actual iOS app already, then this is of course worse, but if you have something that works nicely as a webpage on Android with ServiceWorkers and you want iOS users to have some option at all, this is probably worth playing with.
All browsers on iOS are wrappers around WKWebView (Safari, for the most part). You can’t release a browser app for iOS that doesn’t use this.