Yeah, they've answered this question a handful of times already (there's even a group for it):
Basically, Korey felt that Carlyle's vibe didn't fit with the rest of the group and that it was causing rifts - while everyone else would show up for a review and hang out and have a few beers and shoot the sh** and enjoy themselves, Carlyle would be the only one who would be like "let's go, let's get this done, I have to be out of here by this time or that time", etc. and Korey didn't like feeling like they had to rush something out just to accommodate Carlyle's schedule. And Carlyle has a million other things that he has to do (he writes for like a bazillion different websites), and a new "secret project" he's working on, so he asked to take a step back and just be on the podcasts (ACOCO and Blu Tuesday).
Of course, I'm just paraphrasing from the ACOCO where Carlyle talked about it and the Spill Call-In Show where Korey talked about it, so you might want to check both those out to get the full story in their exact words.
Kinda feel like that is saying more then what was actually explained. But I'm totally gonna copy and paste that for the next person who asks what happened to Carlyle...cuz you know...there will always be someone else asking the same question that was already answered :-)