When he saved the entire planet from invasion, what more does a guy need to do?
Problem is we don't see this happen. Which, really, is why Superman should have stopped the Metropolis-end of the World Engine for their plan to work. Because as it is now, Metropolis sees the thing just stop working and then disappear and then some guy and blue and some guy and gray throwing and punching one another into buildings for 20 minutes.
There's no point where Metropolis sees Superman stop something from happening, saving the city/world and then they rally behind him and cheer.