The way I thought it was intended, Amaterasu, Tsukuyomi, and Suusanoo are 3 abilities that come with achieving the mangekyo sharingan, and any other powers (Kamui, Shisui's special eye hypnosis) were special "born with" powers. Though granted, you are right that we actually haven't seen anyone besides Itachi and Sasuke use Amaterasu. As for Obito or Kakashi not being able to use the three, maybe it's because the eyes were split and you need both to perform it? Kakashi especially as a non-Uchiha wouldn't really be privy to their knowledge, I mean who's gonna teach him lol. Sasuke only knows them because Itachi implanted their knowledge into him at the end of their last fight, otherwise who know how long it'd take him to learn on his own.
...yeah hell if I know, I mean they all can perform some shared techniques (izanagi for example was used by Danzo and Obito), it just might be a matter of learning or some crap. Or they just never had a chance to bother with it.