(Bathroom discussion; possibly NSFW) Why are guys expected to put the seat down and women not expected to put the seat up?

While my son was visiting, I entered the bathroom and noticed he had left the commode seat up. He’s a single dad, and doesn’t have anyone around of the opposite gender to make this an issue. On the other hand, I have been with my wife for almost 30 years, and have been fully trained to leave the seat in the “down” position.

I noticed this in the past, also, that the women with whom I have shared habitat have generally insisted that the guys put the seat down after urination. In bachelor residences, this is not an issue, because the facilities are used much more often with the seat up than down.

I was trained told at one point that it is common courtesy to put the seat down after use. Why would it not be the same courtesy for those who sit to place the seat in the “up” position after use?