[riffraff]

It's a matter of habit and personal traits.

I grew up doing homework with the TV on and still sometimes work with a tiny video overlay showing some anime or tv show.

You basically pay attention to a small part of it, and switch focus as needed (pause your task or pause the video). You'll still miss a lot of the video but you just don't care.

I know this is unthinkable to some people but I've met more than one person who does it, so it's not ultra-rare. Possibly related to ADD/ADHD? I don't know.