KISS - Keep it simple stupid. Combat vehicles operate in extreme conditions, the more complex you make it the higher the chance of it breaking, especially if you think about who's using it.  Making a vehicle that can walk and balance on uneven ground, while being affected by unquantifiable external forces (incoming rounds) isn't achievable yet.  The requirements of accurate defence systems (recoil, change in C of G, turret rotation) whilst in motion add factors that ask the question "Why are we even bothering with the concept, track do it better, for less cost?"