I think it has to do with the cubic space your trying to cool. The 4 door Tahoe is a crew cab size plus the large area behind the rear seat. More so with the suburban. The crew cab pickups do have extra ducting to move chilled or heated air So any way to maximize the efficiency of chilled air.
And if you wanted to retrofit this function / parts you could very easily.
And if you wanted to retrofit this function / parts you could very easily.