Why do they use 4WD hatchbacks for rallying?

Answer 1

The same reason they use 2-doors. It doesn't matter what body style the car/truck is. What matters is the running gear underneath.

If an auto manufacturer is trying to push the latest model and it is something they want to reflect what the 'Average Joe' can buy, they'll use the cheapest, most common body style they make to push-the-product, so to speak.

Back in the day of late 60's/early 70's NASCAR, there was a saying "Win on Sunday, Sell on Monday." The same can be said for Rally cars. If you're into those cars and the drivers, then you want to drive what they're driving. Granted, it's not a RACE CAR, but it's the next best thing!