The same way straight guys assume women will be into them, regardless of what the women they want actually want for themselves: male privilege. Clueless straight dudes have little to no experience being the “pursued” gender and guess physical attraction amongst men is the inverse of their own unfortunate socialization.

Certain men assume their way of seeing the world is the way everyone sees the world. Those certain men find it nearly impossible to see the world the way someone with less privilege sees it. Those of us with less privilege have no choice but to contend with the dominant ethos. Those with more privilege can live their lives quite comfortably (and ignorantly) without every having to contend with an oppressed individual’s worldview.

Addendum: Because of the way society fucks up women’s perception of their own attractiveness, many women, conversely, underestimate their own appeal.

Addendum 2: This, of course, all goes out the window when clueless straight women assume their LBT women friends and associates will automatically be into them.