Apple also controls the web browser on iOS, and has specifically avoided implementing features that would allow making useful offline webapps. They also do not

Apple also controls the web browser on iOS, and has specifically avoided implementing features that would allow making useful offline webapps. They also do not let other browser vendors (Chrome / Firefox / etc) publish full browser engines with any of those features on the app store. You can't run any sort of background code (webworkers etc). You can't have a split-view for a progressive web-app on iPad. You can't have notifications. The lack of notifications is a big one, and one of the things that makes such apps mostly non-starters.