of toilet locked

To use the guys toilet at the petrol stations, one (a guy that is) just had to go to the toilet and use it.

To use the ladies toilet at the petrol stations, one (a lady that is) had to go to the cashier to get the key to unlock the ladies toilet door.

Photo of lock taken from LWR

Is it because of this [photo via -netochka-], that's why ladies toilet need to be locked?