Jomison
B747 has auto braking on the main gear as do all large aircraft. If they used the normal braking system, like small plane drivers do, the tyres could rotate around the wheels and break the valve stems.
Second, I'd guess it is the nose tyres, slightly out of round, being slowed by the snubbers in the well. Again, the snubbers cannot stop the wheels instantly for the same reason. Why "out of round"? Sitting on the ramp all night, heavy weights, out of balance.