Probably the same reason that men have lower breast cancer survival rates than women - the common assumption is that it's a gender specific disease, which delays diagnosis and treatment: http://www.breastcancer.org/research-news/20120517

Yeah, I almost typed "immune" before menopause, but that's not entirely accurate. And as you point out, it implies that a pre-menopausal woman having a heart attack just doesn't happen. Hell, my brother-in-law had an nearly fatal heart attack when he was 34 (bad genetics, helped along by too much drinking and smoking). Gender and number of wrinkles are just data points, but not the deciders of who's having a heart attack and who's not when their arm goes numb.