First of all, let's not make excuses for Conor's appalling refusal to send Dustin the charity donation. That money would went through the following day if Conor won the rematch.
So why has Conor failed to deliver on his promise? The answer to that is simple. Conor wants the angry and emotional Dustin to return for the trilogy fight.
Conor knows that calm and composed Dustin is a serious challenge and Conor doesn't want to see that version of him again. So, what better way to get Dustin emotional than to not only refuse to honor the agreed charity contribution but also imply that there is something shady going on with the organization?
As a one time Conor fan I hope Dustin doesn't take the bait and ends Conor's career. This isn't drunkenly punching an old man or attacking a bus. I can not find a way to forgive this. It's a stone cold sober, calculated and despicable act.