It's on most of YouTube streams because Google forces it on devices that lack hardware support, even if it breaks the functionality of the device.

Mainstream support doesn't have to be forced.

Even if half the devices were broken, it would still be more than a third of streams and mainstream.

A lot less than half of devices are broken when playing YouTube, I assure you.

If they stopped forcing it, it would still be the best choice most of the time. It doesn't "have to be" forced to be a major choice. The forcing changes the exact percentage but not the overall picture.