Quoted from PinballTilt:
Is he the one that bad mouthed Gomez and aired the dirty laundry? If so, wouldn't surprise me and I'd have fired him in that position. You make a comment like that and it's not likely the first time and someone like that is a cancer
Wasn't he a contractor? It's semantics, but it's not really firing someone if they don't opt to renew the contract or accept the proposal for work.
That said, Franchi did good work for Stern and it stinks to lose work. But if you're not going to be professional with how you discuss your business partner, then you can't be surprised that they don't want to continue the relationship. Good artists are not hard to find, even if it's a small subset of artists who view pinball as a passion project.