He is charismatic, but you have to realize that if you compare Riley's theme to someone like Barrett, Cesaro, or Miz, it's just not even close. He has probably the top 5 best theme songs in the past couple of years, along with McGillicutty, there is no denying this, and it is a big part as to why he always gets huge reactions.
Kofi Kingston is stuck with no character at all. He's what, Jamaican? That's his gimmick? He isn't even from Jamaica. He has shitty theme music, no presence, negligible amounts of charisma and almost no ability to work the mic. He's good in the ring, that's great. The WWE is an entertainment company foremost, and if you cannot entertain, then you are not good enough to be in the main event scene. Go watch NJPW or something if you want good wrestling, people who watch WWE want to be entertained, wrestling is just one part of that, you must be good at everything if you want to be successful in the WWE.