King K. Rool is an absolutely insane psychopath. Look the things he did in DK64. He wanted to blew up a whole island with a laser machine so he can kill off his arch enemies and all the other animals on the island. He even executed one of the Kasplats after failing to defeat the Kongs.
KKR is for me on the same amount of evil like Ganon. The only different is, that KKR is portrait more in a cartoony way.
I think, that Nintendo themselves have no idea, how to use KKR correctly. Look up the latest appearances. In Jungle Climber and King of Swing he was just a cheap Bowser clone and not even a good one. Maybe that's the reason, why Nintendo does not want to use him anymore. For them, he is just another Bowser.
I mean, look up his latest boss fights: He grew up big, spitted fire balls, had a flying vehicle similar to Bowser's clown cart and only seems to have one type of henchmen: the Kritters.
Nintendo sees him just as Bowser 2 and not as his own type of character. Which is wrong! KKR was created to be his own villain by Rareware.
That's the reason I do not like the current KKR from Nintendo. He's just a boring, cheaply made copy of one of their most popular villains. The one from all the Rareware-Games on the other hand was just freaking awesome! Because for Rareware KKR was this really insane, lunatic with so much style and evilness. Every single boss fight with this guy was different, every single theme with KKR was different, every single plan was different. He was one of the most varied villains back in the old days.
Speaking of villains: Rareware did actually an amazing job with their villains. Not only King K. Rool was really great. Gruntilda, Wizpig, Don Weaso, Professor Pester, Mizar form Jet Force Gemini and also some villains, who actually had a really good concept but had to be turned down because of the instruction of their bosses like the Mystic from Kameo or General Scales form the original Dinosaur Planet.