The Compass View
Zhuge Liang was a ancient Chinese strategist whose current base of fans have ignored his flaws and his frailty for the usual reasons of supporting the "the friendly and intelligent underdog/nice guy."
Fact: Zhuge Liang did almost everything that enabled the Shu State to survive. Unfortunately, that effort was not able to conquer the Wei state.
One man is never enough to change the course of history. Simultaneously, the majority of the masses are focused on the end-results regardless of the situation.
One Possible Reason
Another Possible Reason
Concurrently, there was always a chance that the Shu's court was penetrated by political collaborators, agents and spies from the other states whose goal was to subvert from within.
None of these incidents were never recorded. This possibility could have also prevented Zhuge Liang from ever succeeding.
The Possible Grand Reason
In some historical instances, those mentioned points have usually caused the downfalls of his campaigns.
Retrospectively, we would never know what were some of the undocumented causes behind the collapse of the Shu state.
Psychologically, many of us admired and adored the ever-persistent underdog. However, history only awards the victors and the founder of the Jin dynasty became the winner.