Basically the apps are developed by much the same people that are doing the web dev. And those are very much Mac/iPhone users.
Thus they are barely aware of what is going on with Android.
Hell, the Allo boss basically made claims that made zero sense for why it didn't integrate SMS into the message timeline.
This while Android users have been screaming for a Google brand messenger that integrate SMS, and Android provides a SMS backend that any app can talk to.
This seems like quite a profound stretch. I'm not even sure what the parent is talking about regarding YouTube hardly taking advantage -- it takes great advantage. The Android platform is absolutely its benchmark implementation. And it's completely native, so this isn't a group of iPhone devs doing it on the side.
This notion of the forgotten Android implementation from a bunch of Apple fans seems almost quaint now. While it was true years ago, at this point any shop that does that sort of thing is guaranteeing themselves doom. It isn't an after thought.
So why cripple PiP on iOS and bury it on macOS?
• On macOS, you have to have to menu-click on the YouTube web player TWICE to bring up the PiP option [1]; why not include it in YouTube's own menu or control strip?
• on iOS, you could access PiP by visiting YouTube in a browser, or pasting a YouTube link into certain sites [2], but they seem to be actively locking down on this. There are third-party apps that let you view YouTube in PiP, so why is it not in the native player?
The menu on the second click is Safari menu for the <video> HTML5 element.