Werewolves have grown too fond of their rich lifestyle so much that they have relaxed their guards and stop their natural evolution. The modification might have enhanced their powers but they have lost the will of growing for survival and dominance after learning about the decline of nobles. A safe environment makes you lazy and susceptible to danger.
On other hand nobles had fallen from power so they are constantly on guard in face of any possible extinction of their race. The danger of extinction made them strong as they trained in order to survive in the world which is no longer under their control. I believe this is the reason why current clan leaders were able to grow so strong in such a short span.
I believe it's the change in mentality which has ruined Werewolves and strengthened Nobles.