I think it is because guys are selfish and sex obsessed :) Sorry to all the males :p
No need to apologize. I think that has a lot to do with masculinity and maybe you don't, but many women do like those two traits.
1. Depending on the way you look at "selfish," most women I know like guys who have a drive, who has goals in life, who has something that he's willing to do what it takes to achieve. At times, that means being selfish and putting things aside in order to work towards a bigger goal. So long as the guy still maintains control over his goals (instead of them controlling him) then I see no problem there at all.
2. If guys weren't sex-obsessed, relationships would cease to exist. Think about it... despite the fact that there is more equality now than ever, for the most part it's still up to the male to initiate the interaction that leads to a romantic relationship. With rejection, fragile egos, lack of confidence, etc., it's almost necessary for that sexual drive to be there in order to push through those mental obstacles and gather the cajones to talk to that woman you're interested in.
Now, I understand that you mean selfish and sex-obsessed in different ways. However, I don't call those people "men." I think those guys who just wanna have one-night-stands and have no respect for women and themselves are really "adult boys" rather than "men."