I think the main issue stems from this:
To push turrets, you usually need a coordinated effort. Sometimes this is a 5man roll, but sometimes it involves having a harrasser or 2 push side lines, pull the other team out of shape, and then a push. In short, it requires intelligent, coordinated action. If no one on the team takes leadership, as often happens in pub games, individuals decide to farm more until they can win without good coordination.
The solution to people not behaving in a coordinated way is not to QQ at them. It is to show constructive leadership and help the team win.