There are a few reasons why bathroom light switches are typically located outside of the room. One reason is for safety purposes - it's easier to turn the light off from the hallway than it is to walk into the bathroom in the dark and fumble around for the switch. Another reason is so that people who are using the bathroom can have more privacy; by keeping the light switch outside of the room, people don't have to worry about someone seeing them in a compromising position when they're turning on/off the light.