Does anyone know? Was this a decision made solely by Prince, or were the band members eager to do other things?

Probably used The Donald's favorite line.."YOU'RE FIRED!!!"

As far as we know, it was Prince's sole decision. Wendy and Lisa were particularly upset about it. From their point of view, they are quoted as saying that they wanted Prince to focus on just the music and go in a purely musical direction. Prince, however, wanted to expand the range and become, as W&L put it, an "all-round entertainer". They felt this was a waste, but we all know how it turned out.

Wendy and Lisa were going to quit the band in July but were talked into staying. They loved playing in the band but it was getting harder on a personal level because he put them in a position to choose either Susannah or him. Of course they sided with their sister (before someone says anything yes I KNOW that Lisa isn't her sister but they may as well be). They wanted to keep going in the Revolution but Prince fired them along with Bobby Z. Doctor Fink and Brownmark were asked to stay but Mark decided to leave with the core of the Revolution.