It's a difference in philosophy for the most part. Google are an advertising company first and foremost, they'll do whatever is best for the advertising industry and to Google allowing every Tom, Dick, and Harry on the web to shove notifications in people's faces is great. Apple take a more paternalistic view, they see that push notifications in the browser as a feature that's often abused and so remove it entirely as to protect their user experience from annoying behaviour that's outside of Apple's direct control. Notifications originating from apps in the App Store in theory can be vetted much more closely and removed if they're deemed to be spammy.

Neither is intrinsically right and I think it's good that there's choice, what's winding me up is this idea that everyone should adopt the Google model unquestioningly as though Google are a standard unto themselves. I'm very much in the Apple camp, but it's not out of any love for Apple and more that I don't like the advertising industry and want to keep it as far away from my life as I realistically can. To me push notifications are like popups in the '00s, yes there's legitimate uses in limited cases but abuse is so widespread I'm going to treat every one as guilty until proven innocent.