The trouble, then, would be that YouTube's implementation is either broken or nonexistent. (We can tell this because if it did exist and did work well, then there would not be complaints.)
Of course not; how could we ever be sure? We're dumb users; inspection of details of interactions between our browser and a website is a black art.
"Youtube doesn't work" is the default apparent failure mode here; and this failure mode does not provide even a PC LOAD LETTER way of going further.
(It'd be nice if it were transparent or always worked, but again: It is simply not this way. And again: We can tell this because of the complaints, and of the storied workarounds.)
Some error handling, data logging, tied to user reporting could do a long way here. I've never looked under the hood of YT, so I have no idea of the user journey in these cases. The full picture would be only visible from the Google side anyway and it'd be up to them to figure out what combinations of capabilities are causing trouble.
The trouble, then, would be that YouTube's implementation is either broken or nonexistent. (We can tell this because if it did exist and did work well, then there would not be complaints.)