It's worth looking back at the White Paper of 2003, the Future of Air Transport and the forecasting exercises done at that time to see what a different world that was. At a rough guess the DfT was at that time predicting around 27-32m at Manchester by 2014. They said that the existing terminal capacity is 30m and existing permissions would take that to 40-45m.
So what happened? MAN is at 22m instead of 27-32m. The national forecasts were hopelessly wrong. The global financial crisis destroyed most of the growth. There is a long list of culprits among whom I suggest the managers of MAN come rather low down on the list!