After the season he just had on his new long-term deal, Graves would have to play his way back to earning that kind of team commitment before a team would be interested in helping out the Pens. Besides, the Pens lack the depth to comfortably move him.
"But the Pens could just go land another defenseman in free agency/trade!"
Well, no doubt so can the Utah franchise to flesh out their own top seven, solving what was evidently their only reason to consider this trade in the OP.
This used to be a dumping ground franchise for bad deals, but those days are now over. Graves doesn't have a ton of trade value. No one is motivated to take on the risk that he doesn't bounce back. He's going to need to improve in Pittsburgh before a move becomes viable.