Why? Perhaps because there is just too much pain and suffering for a heterosexual man in having to share a political milieu with feminists.
To give you a flavour of what left-liberal men have to put up with, consider this Open Letter to All the Liberal Straight Men by a feminist calling herself Earlbecke.
Remember, Earlbecke is writing to the men on her own side. She is not writing to criticise and annoy conservatives like myself, but to address the average left-liberal, politically correct male.
Her first six words begin in a friendly tone: "Dear Straight Guys, I respectfully submit...". However, that's it for friendliness or respect.
She proceeds to tell male leftists that they are actually not understanding or sensitive individuals just because they show concern or admiration for women. They remain sexists if they show a "specialized sort of attention to women", namely a heterosexual appreciation for women. Instead, they have to change the very way they think so that they see women as people rather than as women.
She then begins her official first point, which is that this is all about her and not about men, so that when she is attacking leftist men their role is to passively listen and accept:
Resist the urge to assert yourself in defense of the male voice. We've already heard it, and doubtless we will hear it again. Save it until we're finished. Do it somewhere else.
Her second point is the same as her first point: that this all revolves around her and not about men, and that what men like isn't relevant and women shouldn't care what men like.
Her third official point is the killer:
3. We are all human beings. We are all similar lumps of fleshy matter that moves and grunts and goes around its daily business. Until you can look at any random woman on the street and see the human being before you start placing significance on the gender presentation, until being human, of any variety, any color, any sexual orientation, any genitalia, any anything, is the nebulous vague default in your mind, you still need to try harder. If you automatically assume a person of unspecified gender or sex is “he”, or white, able-bodied, and heterosexual, that is your problem. And this is why so many of us have no time or patience to try to explain things to you.
She's not exactly a romantic soul is she? She can only conceive of men and women being "similar lumps of fleshy matter that move and grunt". And she demands that we all think the same way. As an instinctive mental default she wants all men to see women not as women but as "its", and to only consider the "gender presentation" as some kind of afterthought.
Point number four is that men have no right to question her on this and that she is "not required to explain myself". Men, she admits, might be made confused, upset or defensive by what she says, but they are not entitled to have "everything placed in a pretty little box" for them. Continued listening, though, is OK.
Number five is predictable: all men are guilty. The only kind of male not guilty is one who "reads the whole list and nods along and then genuinely apologizes for your gender (while not feeling the need to defend yourself by insisting that you do not represent these men)."
So leftist men are innocent if they silently agree to everything, apologise sincerely on behalf of all men, but don't attempt to separate themselves from male guilt.
Now surely, the response of most self-respecting men to all this will be to find a political home elsewhere. Why belong to the left if it means being berated by haughty, condescending feminists for the "sin" of being male and heterosexual?
Earlbecke seems to recognise the burden being placed on straight left-wing men: that of being made confused, defensive and guilty. She seems to think that this is a deserved condition for men.
It is a burden, though, which can disappear in a moment of true liberation when a man decisively rejects the politics of the left, and this is what political men in general appear to be doing.
(There is more on the same theme in an interesting post by Julian David.)