I rarely had a bedroom lock and iv been through a few shared houses.
If I couldn't trust the other occupants in a small house then it was time for one of us to leave.
I can't ever recall a bedroom door without a lock be it in houseshares or family or friends houses I would call it very abnormal. Even in your own home with family there are times you want to lock the door of your bedroom.
I would see it as highly unreasonable for a LL not to have locks and the reasons given are bordering on tin foil hat stuff.