1970s elections are considered most fare election in Pakistan history, ironically they were most divisive election not just in Pakistan's history but probably in history of democracy. PPP won overwhelming numbers of seat in West Pakistan, not a single seat in East Pakistan, they hardly had any candidate in East, same was true for Mujib's Party. Mujib ran election campaign on very nationalist (aka that 6 point agenda) and Bhutto ran the opposite.
You are right people did spoke, unfortunately two very different voices. 1970 election results showed a very divided Pakistan, you just cannot blame Bhutto and put everything else under the rug. Bhutto largely did what he promised in campaign so was the case with Mujib, they both stood to their view point on which they won election by land slide... Seed of power reside in West Pakistan for 25 years(before 1971), that's why Bhutto was in position to take a stand, I don't know that exact number but entire top leadership of Army was from West too if not majority of soldiers, where as East had bigger population. Army stood with their own one(aka West Pakistani), for a reason. If I am not mistaken Mujib was more interested in being CM of East Pakistan than PM of Pakistan, which you can see from his campaign and 6 point agenda... This division would have happened anyway if those 6 points would have implemented.
The seed of divide was planted long ago. Bangalis did not wanted to live with Pakistan, that was very clear in 1970s election. Lot of that has to do with how Pakistan was run in those 25 years, Ayub 10 years rule, made it clear to Bangalis they will have hard time. They were not welcome into the most prestigious institution of Country aka Army, not just welcomed, they were discriminated, since they were not broad and tall enough. This is just one example, they wanted to keep their language and culture intact and wanted fair share of power and economy...
Reality is East and West Pakistan was one of the most unnatural country, they had nothing in common, it was hard to keep them together. They were not physically connect, had no common culture, language, even currency, top that with the fact that your main enemy is between the two parts of the country. Which other country was/is built like that??