Two gals and one bathroom, why do they go in pairs?

I just have to ask because it is a curious act some women take. I am at some establishment where the restroom is single use. However, you see two gals going to it and they both go in. It is single use, if one is going to answer nature’s call, what is the other gal doing, standing over her? Does it take two to put on makeup? I do not know any guy who would go into a single use restroom with another guy even it if were just to wash their hands; they would wait until their friend, etc. cam out, then they would go in. Why the run in tandem for women?