If you notice that the front wheels pull less and have less resistance than the rear wheels, there's a logical explanation.
The front wheels act as a kind of "helper motor" for the car – they are not true drive wheels.
Their purpose is to reduce resistance in the front wheels and to assist the rear wheels of the vehicle.
They are not meant to pull like the rear wheels, which is why, on many models, you can even stop them with one hand without much effort.