Yes, you are right. Military alone was not responsible for the 1971 debacle. It was a collective failure
But the question is that why does the Army, the country's dominant power center, always support the "wrong" side?
They always support unpopular leaders against the popular ones
Mujib was more popular than Bhutto, Army supported Bhutto
Bhutto became the most popular leader of (west)Pakistan, Army killed him
Benazir was more popular than Nawaz Sharif, Army supported (rather created) Nawaz in 1980s
Nawaz won 2/3rd majority in 1997, Army imposed martial law and exiled him
Nawaz was more popular than Imran Khan, Army supported Imran in 2018
Imran is the most popular leader in Pak ryt now, Army is supporting PDM against him
The Army always goes against the will of the majority to retain their role as country's dominant power center
The Army is not willing to concede the political power to the people of Pakistan
We have already lost half of the country because of this, and we may lose what we are left with