They used to claim that it was genetic. I think the upward curve shows that it is more likely the result of brainwashing, at least in recent years.
This is really going to create even more issues for heterosexual men; at some point there will be a Rubicon crossed where traditional male / female relationships will be over and men will not want to ever go back --a lot of them are there now. This is going to be a real problem for our society and others around the world. I myself (male, heterosexual) have chosen to remain single for the rest of my life. I had many girlfriends when I was younger, and I was married for a bit. I am no longer satisfied with the situation.