I don't think that money doesn't matter at all, but I do agree the "optics" are probably JP's main driver.
After just winning a conf tourney, making the NCAA, and being extended -- to fire him after the season would look to outsiders as extremely impatient. With JP trying to make part of ISU's brand and value proposition to good coaches as being steady and reliable and NOT hyper-reactive, he isn't going to start chopping off heads like that.
For as bad as this season has been so far, firing Prohm after last season's success would have been f*cking idiotic.
We would have gotten absolutely torched PR wise, and rightfully so.