Safari's support for anything that Apple doesn't seem to use on their own web properties, is really crap. WebRTC and WebSockets also been lagging behind for a long time and when they catch up, they tend to have very buggy implementations.
What incentive should they have to make Safari a capable browser? Who would profit when developers can build PWAs instead of paying the Apple Tax?
Apple and Google's business incentives are in opposition. Google benefits from web apps replacing iOS apps, while Apple benefits from iOS apps replacing web apps.
Native apps can offer many benefits (such as power efficiency), but I expect that business reasons are equally if not more important.