Comment by pathartl

Because it's genetic. It's something that develops during sexual maturation, it doesn't just pop up. My SO is the third generation in her family that has Endo. Women will have flare ups where they will be in excruciating pain during one menstruation cycle, and the next might be a non-endo's idea of a bad cramp, so it's often misdiagnosed as severe constipation, appendicitis (even though the pain is almost always on the right side), or they're given the "it's just in your head" treatment.