The demand is there but it seems airlines are happy for us in the West Midlands to travel to other airports from where it is cheaper for them to operate from. I for one in the past two years have flown from LTN, EMA, LPL and MAN primarily because there was no direct flight to where I was going from BHX and having researched connecting flight prices from BHX, it was considerably cheaper to do so. Although connecting options to European cities are readily available from BHX with LH, LX, AF etc they are often quite expensive. I'm flying to ZAG next week, cheapest connecting flight from BHX was around the £270 mark, BA from LHR direct was around £100. I'm not saying there should be a BHX-ZAG flight but that it easy for me to get to LHR and cheap to fly from there for this journey, even factoring in the cost of getting to LHR. Total journey time via LHR is little different to the flight connections I was offered by LH from BHX. Am sure there are thousands of other similar examples to more obvious destinations like MAD, LIS etc that other UK airports happily manage to maintain services to.
I have always said that BHX's central location and pretty good transport links are both a blessing and a curse.