I think it depends on what you mean by masculine. A woman who ACTS masculine, or a woman who LOOKS masculine? I feel they are two completely different things.
Some guys are attracted to women with short hair. Some don't mind if a woman is taller than them, or has wider wrists. Some women have a stronger jaw line than most men. I've seen a few men above saying it comes from a place of personal preference.. I'm gonna say to an extent.. but I'm also gonna go against the consensus here and say it COULD be closet homosexuality (not saying this is the case for you), or actually is low T/hormonal imbalance. I say this because as men, we are not biologically programmed to be attracted to these types of traits. We look for submissiveness, so we tend to be attracted to women who are smaller and more fragile. We have hundreds of years of evolutionary science to back this up. So unless humans are branching off into a new evolutionary path, it sounds like there is something bio-chemically off (most likely low T).
Now, let's say you are attracted to women who ACT masculine..
From a psychological standpoint, it could just be you wanting to hangup the "boots" and have a woman take control for awhile. Maybe your sub-conscience is tired of playing big bad "alpha" all the time. You might not be conscientiously aware of it, but maybe you are purposely putting yourself in situations where you meet women more on the dominate side, because for lack of a better term.. you're "lazy", or actually have low T/hormonal balance. It could also be social upbringing, or how you were raised.. but I'm still leaning towards the low T.
You should just get a T test. I'm almost willing to bet it's low. Especially if you already suspecting it.
Also, I mean no disrespect from any of my comments above. Just calling it as I see it.