In the case of smokey black, I'd say it's because a black horse w/ a cream gene is still a black horse!
Smokey cream, I wouldn't have a problem w/ them giving a name to. But they DO register them! They didn't at one time, and at that time I disagreed w/ them, but now they'd be registered as perlino. And I (and I assume most people) can tell the difference between a cremello and a white horse.
AQHA has done away w/ their white rule, and the only other breed they let in is TB, and the horse is appendix depending on how much TB it has.
I'm not fast enough again!