That was my first thought too and it probably the number one reason but at most places women normally have to wait in line to use the restroom so having someone to talk to while you are waiting is always nice.
I've never gotten that concept either. I much prefer to go alone. I don't really like talking over tinkling noises (unless it's a piano that is doing the tinkling ).
I go alone. This irritates a few female friends I socialize with. I think it has something to do with them not wanting the men to think they really do need to relieve themselves. If we go together, maybe they'll think it's just to powder our noses.
One of these friends, married for 20 years, has NEVER passed gas in front of her DH.
I think we do it for safety also. I mean I have two dds and well if I gotta go I make sure to drag them with me because if I gotta they usually do too.
I think that is where we learn it.