Indiana Jones ride question?

It isn't the walls moving the designers wanted you to notice, but the boulder. The boulder is essentially a fixed point, and the walls moving backward provide the illusion that the boulder is getting closer to your car.

what i probably think is that the engines that get the ride vehicles moving are already doing enough things like moving up and down, going fast going slow and stoping. it probably would have taken to much tim for the engine to switch all its functions to reverse just to go a few feet and switch as its functions again just to make the scene more dramatic.

My guess is money. In the long run, it's probably easier to maintain the walls than one of the cars.