I think it was explained in the past by HT himself...
Most people playing the game do not use an analog control for brakes. Meaning either on, or off. If HT set the aircraft's brakes to have actual real life pressure, due to the nature of how they are controled, most of the people landing would flip and destroy their aircraft.
So for sake of gameplay, it was made so the effectiveness of the brakes were to NOT lock up the wheels so as to not introduce that particular nasty problem.