I'm talking about my family members and girlfriend playing music or movies in a room where I have a great stereo system, and not connecting to it, even though they are already paired and just need to click the icon.

I think you hit the nail on the head- people think a big stereo is for volume levels, not quality. They will obviously switch to it when they want things louder, but often not before.

You must not have normies in your life. I'm subjected to cell phone and laptop speakers constantly.

Not sure what your definition of normie is, but that's been my experience across a fairly wide spectrum of US society.

When I went to public high school in rural America, pretty much everyone I knew owned some sort of headphone/speaker system, and they would be used at every party / larger gathering where audio was important.

It depends on the context though. Obviously if someone is just sharing something casual like a Youtube video on their phone, they're going to use the built-in speakers.