Maybe it's because their immune system has been challenged and as a result strengthened during the lifelong course of battling- and winning- said infectious afflictions, that they become stronger and better poised to endure later-stage illnesses. Well, that and on the whole they tend to take fewer risks and care better for their health than their worse half.
Give me a grant and I'll come up with and publish the truth of the matter. But my findings, I just have a hunch, will require lots of investments. Send. Check. Now.
I thought it was because they have two X chromosomes, and men only have one. There being hardly anything on a Y.