because they are stupid.
Actually, the only reason I could possibly think of is that you could push your car so hard to one side, that it would break the studs that connect your strut tower bar to your shocks (since thats what connects the two anyway) and then your shock would come out, and then all hell would break loose. But this would have to be one hell of a push, and since its only a cavalier, I don't think he should have anything to worry about.

Go to another shop.