While Nasus was quite a terror in previous seasons, stacking is not worth as much now.
In today's Meta If you don't have a top laner that is omnipresent with teleport, your team is in a pretty bad state.
Nasus needs a lot of stacks to be effective first and by that time, their jungler and top laner got already 3 drakes.
So why not make him a juggernaut too? He has all the aspects of a typical juggernaut: Tanky while dealing a good amount of damage, and yet still immobile.