The defendant is charged with fraud. The only real dispute for trial is mens rea. The defense does not intend to contest that the transactions occurred in the manner the prosecution alleges.
To establish the fraud the prosecution anticipates needing to introduce extensive, dull, and potentially confusing evidence of the underlying transactions.
Defense counsel knows that a dull and confusing prosecution case can benefit the defense, potentially leading to an acquittal or a mistrial. The prosecutor knows the same.
Here there is room for a third option. The defendant might proceed to trial, and receive no leniency if he is convicted. He might plead guilty in exchange for leniency. Or, his counsel might propose to the prosecution that they preserve a trial on the mens rea issue, while stipulating to the complex financial facts, in exchange for conditional leniency should the defendant be convicted.
The prosecution should prefer this to a full trial with the accompanying risk of acquittal or mistrial resulting from jury confusion. The prosecutor won't prefer this to a guilty plea that offers certainty and resolution after a forty minute colloquy. Accordingly, there is room to negotiate for conditional leniency. Leniency less favorable to the defendant than what he would secure with a guilty plea, but more favorable than no leniency at all.