I always figured it was because men were stronger and had a better shot a swimming long enough to get picked up later, except in the case of the Titanic where it was too cold for anyone to survive. Look how long those poor guys from the Indianapolis lasted even with sharks attacking them.
Plus I think the values of Women and children 1st are important ones to pass on. What kind of society are we if we are constantly thinking only of ourselves. The other day I took my daughter to the library. I have been slowed by a couple car accidents so my daughter got ahead of me and to the door 1st. She saw an old lady making her way to the door with her daughter and mine saw they needed help and opened the door and held it for them. They both said thank-you and I saw my daughter smile, I caught it and when we got in the car I thanked her for opening the door and holding it for them and I asked her if it felt good, she said yes, and I told her she even got paid with a Thank-you and asked her if that made it feel even better which she said yes to. I told her people might not pay her with a Thank-you everytime but that is why it makes it more special when she gets one. Solid life lesson accomplished.