it's natural for a mother of most organism to look out for the safety of her offspring. Humans are just like any other animal...beneath all that 'higher thought' crap, we're just operating on instinct/ Parents set curfews because they want you to be in a safe and sound environment.

Some just push it because they're the organisms in the species that seek even more protection for satisfaction. They get happy when you're safe. They want you to be safe so they don't have to worry or anything...

idk some are just overly-protective, though.