The reason is that the weight on the front left and front right of the car is NOT equal..

Same goes for the rear.

You have to adjust all four corners individually to your liking - as they will need some tweaking to get right.

This all assumes that you are on a level area.

Also, except for visual purposed, identical l/r right height is not important - cornerweighting a car usually results in slightly uneven l/r heights....