When you move out of your parents house you can have a lock on your bedroom door only you can get into. When you live in your parents house, you don’t get to turn it into a sublet and put your own lock on the door, unless your parents sublet the room to you. You can think it’s disgusting. It’s probably just your teenage hormones.
Privacy for a minor does not involve locking their parents out of their room in their own home, full stop. What you’re advocating for is that a minor should be allowed to do whatever they want in the name of privacy, and that’s just horse shit. Full stop.