Bathroom etiquette

Why can't women lock their bathroom doors?!? Twice this past week I've opened up the door on someone. I was in the faculty bathroom on Friday and it's usually very dark in there. So I went to push open the stall doors and bang, there's a teacher sitting there. I freaked out and was so embarrassed! Thank goodness she quickly covered up herself or I would have been a peeper. Luckily, she teaches like 4th or 5th grade so she's upstairs. That way I won't be running into her all the time. This happened again at the restaurant yesterday. Strangely for a nice restaurant, their bathroom was so tiny and only had 2 stalls. Beth told me to try and push the handicap stall one so I did and woah nelly, there was someone in there! I thought that maybe the lock was broken but when I went in there, the lock worked. Why is it so hard to lock your door?