US did help Pakistan in all possible ways. It blocked UN action against Pakistan for the genocide it committed, sent military supplies and encouraged countries like Iran and Jordan (which were US allies at that time) to do the same, shielded war criminals from prosecution, sent battle groups to threaten India and so on. In short, it did everything just shy of sending it's soldiers to fight along with Pakistan (which it could not do due to Vietnam War). Final help it did was to reach candid agreement with USSR and India that West Pakistan to be spared. USA is the reason today Pakistan is still on the world map. What more you wanted it to do?