Given what I've seen I just figure like 95% of all women in the scene are bisexual... Or pansexual... Or whatever it is called these days.
There is something sort of hot about an absolutely one sided relationship where the sub LOVES and is ABSOLUTELY ATTRACTED TO the Mistress, and she is a lesbian, with a lesbian lover. They sort of tolerate their slave's sexual antics, but really they deny him because at a fundamental level, they aren't interested in him at all.
They use him as a service slave. They keep him naked and in chastity because they know it's a fantastic way to control him and keep him in line. It's easy to whip his ass on a whim when it's bare, and flick him in the balls when they are on display. They know he CRAVES the chance to watch them naked with each other having something he's not allowed to have - sex. They use that to tease and torture him, and as another vector of control.
He's thrown a bone once in a while just to let out a little steam keep him from exploding, but this is done by the Mistresses more for maintenance of their property than anything else. They don't find his releases sexy, and they make the whole thing humiliating for him and gross. Which is exactly how they regard it.
Maybe they were slighted over the years by men, and this is how they get revenge. Maybe they always thought cocks looked weird and a free swinging cock in their house will never do, so they keep his caged.
But.. I dunno. Is this practical?