They are not necessarily bad at math, but they probably aren't electricians or EEs or have ever needed or been asked to calculate how much power a cell phone charger uses.

Mom/Dad used to unplug things and turn lights off, so they do too.

I think it's also just how people start acting in situations where they can't control anything that would make a difference. In the presence of an issue you can't solve, if you can do something, even if it's small and won't really help, sometimes it feels good to at least do that. Being able to address the anxiety even a little a bit still might be worthwhile.

They don't know it doesn't help. That's what you're missing.