How about pure economics?
Needs the main leg length for landing to ensure tail clearance, but whats the point of a long nose leg? I suspect for each cm you lengthen it, it would have to be proportionally stronger, have more bracing around its mount in the fuselage and need a larger nose gear bay (=less room for other stuff!)
Just needs to be long enough to ensure engine clearance on taxi, the flip side being if you raise the nose far enough then you may decrease the ground visibility segment that is important when the fog is around and you are trying to depart.
Engineering - So many variables!
Last edited by Cough; 17th Oct 2011 at 20:55.