The difference in markets between BHX and MAN is simple and it's geography, MAN is situated in the middle of 4 major urban conurbations, Merseyside, West Yorkshire, Greater Manchester and West Midlands. Add to this the significant other urban conurbations or Lancashire, Cheshire, Staffordshire and it's easy to see why the market for MAN is larger than of BHX.
Very true. 70% of passenger traffic at MAN is nothing to do with Greater Manchester and 83% of all passengers though MAN are tavelling for leisure. The city of Manchester itself can be as vibrant as it wants, but the success of MAN airport is really driven by the holiday plans of Northern England and how well it competes with airports like LPL and LBA who are trying to serve their own local markets. Likewise, economic regeneration in the city of Birmingham won't change the fact that you get to LHR in under 2 hours and so BHX is competing with one of the biggest airports in the world - always an uphill battle when price and frequency are important to the customer.