Why is homosexuality popular?

Why would a guy be expected to be gay if he doesn't have a girl friend, but very few would expect a girl to be lesbian if she doesn't have a boy friend? Why would people think quicker of male than female homosexuality? Why do people talk about gays more than lesbians? Is it so normal for girls to be depicted as lesbian because of their "female" nature (when girls holding hands will be quicker considered as just friends rather than partners)? Why would people rather believe that a single guy is gay than just unlucky with finding a girl friend? Why has male homosexuality become so widely spread, even in societies that originally banned (or still ban) it legally (at least officially)?