If worn, what can cause excessive heat buildup from a reduced ability to absorb and dissipate heat, possibly leading to loss of brake response?

Brakes are designed so brake shoes or pads rub against the brake drum or disks to slow the vehicle. Braking creates heat, but brakes are designed to take a lot of heat. However, brakes can fade or fail from excessive heat caused by using them too much and not relying on the engine braking effect.
Excessive use of the service brakes results in overheating and leads to brake fade. Brake fade results from excessive heat. causing chemical changes in the brake lining, which reduce friction, and also causing expansion of the brake drums. As the overheated drums expand, the brake shoes and linings have to move farther to contact the drums, and the force of this contact is reduced. Continued overuse may increase brake fade until the vehicle cannot be slowed down or stopped.
[Commercial Driver's License Manual]