Do computers emit mediocre sound because users don't want hearing tests?

No, that would not work.

First of all qualified hearing tests require a controlled environment sanitized against sounds. That means a hearing lab with a sound booth and specialized headphones that do a better job of eliminating noise for the purpose of facilitating a hearing test.

Secondly, hearing tests perform a frequency test in different ranges, directionality, and volumes against each ear separately. There is no way for the test machine to know what a person hears without participant feedback because hearing is both a physical and cognitive function. That also means participate bias, such as hearing phantom beeps during the test, and controlling for such.

Thirdly, various groups have tested in past for advanced speaker products that produce ranges far beyond human hearing. I once owned Sony headphones with a range of 11-80000 Hz. Humans only hear from about 15-22000 Hz. The point of the extended range is to provide a more ambient experience through silent noise collision of real world ambient sounds, but that only works if the given media emits in that extended range.

Finally, since hearing is half cognitive people process audio somewhat uniquely and thus enjoy and preference different things. Preferences are not accounted for in auditory hearing tests, because that isn't the point of those tests.

I think it wouldn't have the impact you'd expect unless your hearing is actually damaged or unless you're using headphones with their acoustic characteristics well-mapped. The acoustics of the room you're in would matter more, and those are constantly changing.

To accommodate that, you'd want to do an acoustic characterization of the room, not the listener.