Very likely that any added weight capacity would overwhelm the CCC of the unit or the frame would be out of balance / loaded in a bad way and you could have more failures.
They are balancing the capacity of the frame and the CCC of the unit with everything else on a giant sea saw that can have varied loads. The current placement is likely the safest and given the relatively low CCC of the units moving the wheels back further likely offers no benefit and perhaps could be detrimental.
Then again, maybe the guy that designed it is a jackass.