Because someone actually demanded it.

Dean stared at the cube in disbelief. They expected him to carry around a cube with a pink heart on it?

The energy beams changed his mind. He rested, staring at the scorched cube.
Then, using a marker he'd stashed, he drew a little black Impala over the heart.

He was sorry he'd bothered when the furnace opened for his faithful companion.
He'd get that bitch GLaDOS for this, pie or no pie.