Other mistake: When the camera is close up on McQuade, you can see the cylinder of his pistol is empty.
Continuity mistake: At the end, when Luke goes to shoot a dynamite arrow into the ground at the car, there is no kind of explosive propellant on the ground. In the close up, there is suddenly a pool of flammable liquid.
Answer: Various reasons, but mainly to drive the Dukes out of Hazzard County because the family have been foiling his schemes since his and Uncle Jesse's bootlegging days.
Captain Defenestrator