I think a lot of gay men say they're "straight-acting" because they're afraid of the consequences of being too gay. Femmy guys bear the vast majority of homophobia in society and so it's no surprise some would identify with this "straight-acting" internalized homophobia silliness.

Also, homos who do not "act gay" are basically impossible to separate from the rest of the world until you a) live next door to them b) see them with cocks in their mouths. These guys go uncounted when people think of homos.