>>149455609 (OP)The actual psychology behind it is that lesbianism is closer to the modern cultural norm and so it has a broader range of acceptance. In modern western culture it's expected for women to be more openly affectionate, emotional and touchy., however over the past 150 years or so, masculinity has culturally trended towards 'hardness'. (i.e. lack of open affection, emotion, or touchiness). All those things in men where, for a long time, increasingly considered undesirable, to the point of even tangtential things like say dancing or poetry or saying "I love you" out loud being somehow "gay" or some "pansy" shit.
What this ultimately means is that female-female relationships, even totally straight ones, can involve the girls being all over each other. Straight women can cuddle or hold hands or get drunk and make out and most people aren't going to care. Female-male relationships also cause no fuss, because there is something of an exception given to males for the above "showing affection is pussy shit" if it is done in relation to a woman, the woman is affectionate so it's okay for a guy to do otherwise 'iffy' stuff for the sake of their girlfriend/wife/etc.
But male-male relationships end up with two people who society expects to not be affectionate. Neither one of them is supposed to be overly physical or emotionally expressive and so both of them doing so with the buffer of a female presence is jarring.
tl;dr all lesbian shit can be written off as "women, amirite" but gay shit acts more directly against the expected norms of recent social acceptability. Making lesbians a much, much safer less objectionable choice for any network/studio to include.