Star Trek was aimed at a later time slot and there fore a more adult audience. Batman was exremly popular complete with POW and WHAM balloons at the time. I remember the talk about it in junior high school at the time. Remember this was a 3 network world at the time not a 300 or even 30 network world. And Kirk Uhuru and Mannix were considered scandalous at the time for their racial commentary. That isn't something that would have been acceptable in a mainstream show aimed at younger audiences. If Batman went there it probably would have been pulled from some markets.I mean, the whole Kirk/Uhura thing happened, a Batman/Catwoman fling could have the same impact. I mean, Eartha Kitt allegedly had a threesome with Paul Newman and James Dean, I count that as a massive fuck you to 1960s social mores - if there's someone that could outdo Nichols and Shatner in getting crap past the radar, it's her.
Noir didn't sell well then. You want dark you watched the Evening News with the days body count in the upper corner of the screen.