I suspect that both Turtle and Phil are correct. In the case of the BHX charters we don't know the passenger demographic - they may be overrun with Chinese car enthusiasts eager to tour historic assembly sites. On that basis MAN hasn't a prayer! I suspect that the reality is that the relative proximity to London plays a significant part, which is very tourist specific, and less relevant for the business traffic that a MAN flight would hope to attract.
The impact of the airport these days is overplayed, especially on this thread. Yes they can play a big part in getting on an airline's radar, and highlight possible gaps in service that an airline has an opportunity to fill. They can also offer start up discounts and that sort of stuff, but in the overall scheme of things that is small beer as a contribution to a route's profitability. However once those 2 objectives are achieved the bulk of the case rests with the airline - do they have spare aircraft to operate the route; is the route likely to be more profitable than the current route portfolio if another route needs to be dropped to accomodate the new one. Don't forget that even on a route that ramps up quickly it probably won't be profitable for a couple of years due to start up costs, so needs to have a strong case for supplanting an existing currently slightly profitable route - the whole 'jam today' argument.