This is something that I am truly starting to believe. Masculinity and machismo are seen as negative traits more and more often, in the media especially, but also in western society as a whole.
This goes beyond the realm of strength and muscularity. If John Wayne, Paul Newman, Johnny Cash, Clint Eastwood, men regarded to have embodied masculinity 40 or 50 years ago, were to start appearing in popular media today, they would not attract much attention. Instead people like Justin Bieber, Joseph-Gordon Levitt, Jared Leto are being held up as male role models. Younger males are aspiring to model themselves on these current trends, through their fashion, personal appearance and by maintaining a "slim figure".
I don't believe that every man needs to be a jacked up bodybuilder, but they should at least display virility and that their bodies are actually capable of producing androgens. That they are capable of protecting themselves and their families. Most younger men these days don't look like they could father a child if they wanted to. I truly believe that in less than 100 hundred years there will be little if any contrast between most males and females, at least in terms of sexuality.