It's being reported that there was a major disagreement over the legal strategy that Trump was demanding that his lawyers put forth during the trial. It appears that Trump wanted his lawyers to argue that since there was massive fraud in the election process in those states where he lost, that he was justified in taking whatever action, both legal and otherwise, that he felt was necessary to assure that he would eventually be declared the winner, and would therefore be able to remain in office.
Or else they just realized that he was probably not going to pay them...