Among other things, it also seems like the overdoing of underdoing music comes from wanting audio greeble, or "grain" so as to cover unwanted aspects of other sounds. You can mask a lower recording quality with a little music, or to hide the fact that a live action scene was dubbed over. In those cases music is nothing more than motion blur for your ears.
>Extra Credits
I'll be honest, I've seen only their absolute shortest videos. I struggle to ever want to watch them. They're like the fucking special ed of understanding video games.