Or it's a company so fuckoff huge that one department (Chrome on Android) couldn't get a bug report escalated in another department (YouTube). Eventually they just put in a UA workaround while the bug rots in a backlog somewhere. Common enterprise bullshit.
Or the Chrome on Android team didn't even bother reporting the issue to YouTube and just threw in a cheap workaround. Also common enterprise bullshit.
Bingo. When I was a Chrome developer working on video stuff, we mostly treated YouTube like a separate company. Getting our stuff to work with theirs was a priority, but no more than, say, Netflix. We pretty much treated them as a black box that consumed the same API we provided for everyone.