I don't think this rule is about a woman's life being worth more than a man's life. I think the logic used is the following.
Firstly, it is human nature wanting to save children's lives since they have their whole lives ahead of them, obviously, and the mother is the most appropriate person to take care of them, hence the mother's life should also be saved.
Secondly, women can reproduce and have other children if they are saved.
I don't know if it's how it works but it probably is. Maybe in the past they also considered the idea that women were the "weak sex" and were less likely to survive a sinking ship than men, which doesn't normally apply nowadays.
I personally believe children and their mothers should have preference, and after that, the ones who jump first in the lifeboat should be saved.