All big trucks that I seen have drum brakes.
Disc brakes are much lighter, better for lighter vehicles such as compact or sports cars. They are perhaps easier to manufacture and adjust.
When drums heat up they expand away from the brake shoes. This requires more pedal travel on hot drums to reach the same braking force (brake fade). However, when disc's heat up they expand into the shoes, requiring less pedal travel to reach the same braking force.
