Because lesbians on TV are sexual fantasies. Nobody wants to see ugly women together on the screen. Men will look at pretty women doing almost anything, and women, despite pretended indifference, also enjoy looking at pretty women.
Gay men couples can be unattractive as long as they are not intimate (neither sex wants to see that) and engage in witty, catty banter. Women like to watch gay men talking; it relieves them of the boredom of their marriage’s soundtrack, which is not far from silence. Since real men actually have little to say at any given moment.
Good points.
You’ve given this subject some serious thought. :-)