I don‘t want to know what circumstances make a vehicle‘s brakes lock up, but why? What causes the wheels to stop moving?
Friction. The friction between the brake pads and the wheel brake disc. When the brakes are applied, the pads push hard against the disc on two sides, and cause it to stop spinning. All four discs do that and so the wheels stop moving. Like pinching a plate between your finger and thumb.
The brakes overcome the tires available traction.
EASY 101 - because the driver presses too hard on the brakes causing the tires to stop rolling.
