Dunn, Kearns and Griffey are playing against injuries and a loaded outfield (Sosa, Bonds, Berkman, Edmonds, Jones, et al.). Jiminez is playing against a loaded field at 2nd. The Reds would be hard pressed to include a pitcher when their staff is likely to be considered in the bottom tier of the league.
If Piazza moves to first, who does Larue have to compete against to gain a spot? If Larue produces a decent average with decent power, he has much less competition to hurdle.