they are not going to drive off to EMA to catch a flight to some obscure airport in the middle of nowhere.
People will choose which airport they travel from for a huge variety of reasons, not simply because it is closest to home or has a service to a destination close to where they want to be. It may be down to price, or convenience for others in their party, or parking fees or simply dislike of large airports.
Within a 2 hour drive from Manchester you have LPL,LBA,HUY,EMA,CVT,BHX so plenty of choice: I'm 10 minutes from EMA, 40 from BHX, 80 minutes from MAN but just about to leave for LTN as, on this occasion, it is more convenient.