As Sobriquet said, that's just internalized misogyny, and misogyny in general. If a woman acts more masculine, good for her! She's not acting like a woman anymore! She's trying to "better" herself. If a man tries to acts more feminine, then what the hell is wrong with that guy? Fag. Even women who act "too" feminine aren't taken seriously. A politician came and spoke at our school and said that she was told to put her hair in a bun and wear more pantsuits in order to raise her poll numbers, and it worked.
OP's name ...
It's probably because biology has given men stronger bodies. If you physically act like a man, it subliminally makes people think you're stronger, but if a man acts feminine, then it seems that he is weaker.
The point is that most of this stuff is based on physical traits and how they would work in a tribal society. A male primate would usually survive longer on his own because of defensive and offensive capabilities. The males care for the current generation while the females care for the next. If we're looking at how well someone does in the current generation, then we instinctively prefer masculine characteristics.
By the same token, feminine characteristics make people think the person would be a better parent.
So your ideal mate would be a female body builder? Because she's able to support herself and "survive"right?
Um, no. I'm trying to put forward a hypothesis on why people tend to consider people with masculine characteristics 'better'.
Personally, I don't like girly girls or full tomboys. I like about halfway, and bodybuilders freak me out. Even the less extreme ones. In addition, I find that extremely masculine men seem pretty stupid.