"Behind in implementations"—of non-standard "standards" Google loads into Chrome and then pushes devs to include in their web apps, just like Microsoft did with ActiveX back in the day, and for exactly the same reason: so that not only does their stuff only work on Chrome, but people like you see it not working on Safari and think the reason for that is that Apple is somehow working against them for nefarious purposes.
I don't think that works when Apple have implemented notifications on MacOS Safari for years. So it's not that Apple disagree with the standard, but they don't want to bring it to iOS.
Apple are even on the WHATWG standards body that defined notification spec: https://notifications.spec.whatwg.org/ . And WHATWG is the actual standard, not a non-standard standard. W3C ceded to them a few years ago, which is news to me.
If we were talking about other features, like Web Bluetooth or Web HID which are just drafts on W3C but Google decided to implement anyways, I wouldn't disagree with you. I use Firefox myself, so none of these are supported on Firefox either.
