In macOS, it is Safari, that implements PIP. The sites know nothing about its existence and neither do browsers other than Safari.
The menu on the second click is Safari menu for the <video> HTML5 element.
The menu on the second click is Safari menu for the <video> HTML5 element.
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?
[1] http://imgur.com/a/n8b1l
[2] http://ctrlq.org/youtube/pip/