Why front end shakes when braking?

Uneven application of braking power at high speeds, caused by the heat that is made between the rotor and the brake pad; this is causing uneven stresses in the rotor. Such heavy brake usage aggravates the situation by providing uneven wearing along the circumference of the braking surface.

However, other possibilities would exist with loosened suspension; could possibly be loose lock nut on wheel bearing axle or worn ball joints or last but not least warped rotors that need to be inspected and or resurfaced .