After a few years in the theater, it became common for people to ask me if, or even assume that I was, gay, merely because I was an avid thespian. Even on the national professional level, big name broadway actors are predominantly gay-- Gavin Creel, Jonathan Groff, Nathan Lane. I do not contend that there is any bias toward gay men or against straight men in theater, but conversely, that straight men shy away from theater.
There is, of course, a well-known stigma of femininity, or "swishiness" associated with thespians which I assume is the root of this hesitance, but whence did this stigma develop? Perhaps it has something to do with the art of acting itself. Males in our culture are expected to maintain a stoic disposition, refraining from displays of emotion, especially emotions which involve vulnerability. But to act IS to express emotions, and to express them in a bold enough fashion as to elicit a response from an audience. Maybe this pursuit is seen as too feminine to warrant the interest of a straight man.
I suspect, though, that there is also a more complex, socially-driven phenomenon at work. The theater has long been a bastion for progressive thought, a place where new and controversial ideas are promulgated. This sort of pursuit breeds an atmosphere that is naturally accepting and egalitarian, which may seem especially inviting to people who suffer discrimination elsewhere. This could help to explain the abundance of gay actors in the 21st-century theater. Homophobia may keep some straight men from auditions, while a subtler force pushes the others away. "Homosexual panic" is a term coined by James Joyce critic Roberta Jackson, in an essay on the short story "A Painful Case," to describe the incessant fear of being labeled a homosexual which affects the decisions of both closeted gay and straight men, and I believe that this "panic" is likely another factor which deters straight men from getting involved in theater.