The word was that Dickey had become domineering and demanding and was trying to lead the band. Gregg has a very laid back style, very different from Duane. From what I can tell he liked a limited democracy but was very aware that the band's name was "The Allman Brothers" and had no intention of allowing leadership to leave the "family." Butch seemed to have stepped into moderatorship of the the practical aspects of the band. When you watch the extras from Live at the Beacon the dynamics become apparent. From what I understand they weren't going to be able to keep a second guitarist because Dickey demanded too much "deference and preference." They'd already lost Warren over this and I think they were headed towards losing Derek.
From what I can tell, it was like so many situations I've lived through: Everyone is sitting around shooting the bull and it suddenly comes out that everyone is REALLY uncomfortable with something but they had been keeping their mouths shut. But when the elephant in the room came out, action was needed.
I saw them on their 1999 "Never Trust a Band Under Thirty" tour and Dickey really just wasn't cutting it in a very, very big way. I was terribly disappointed by his performance. Everyone else was dried out and working and he was just not cutting it. Once I found out that he was also being domineering it all made sense.
I wish him the best. I have loved his guitar work over many years.