Seems to be a feeling in the NRA that Wayne would spend every cent they have to save himself. Gresham has always been an ardent supporter, and wants to see them saved. I think that means cutting Wayne loose.
He has basically been in charge for the last 40 years. Without being an insider... it is impossible to know from media reports what is accurate and what is BS, but power and money do tend to corrupt people. Unfortunately, gun rights are currently under greater threat than ever before and it is not an optimal time for a shake up of the most powerful and influential gun rights lobbying group.