Soiling its nest.
I don't think a mission designed to look for organics or life should be landed like Phoenix was. The hydrazine exhaust would saturate and poison the area around the lander, an it has no way of moving out of the contamination zone. It's soiled its nest.
All of the instruments on Phoenix could easily fit on a MER chassis. It's time to standardize Mars landers around a proven design. And it's mobile!