Insufficient interline traffic to justify Gatwick or Heathrow (where the airport operators want big aeroplanes, not 70 odd seaters). London City too many restrictions and expensive; it's been tried already; Stansted and Luton non-runners for similar reasons, city centre to city centre traffic...East Coast wins hands down...you can be in Kings Cross before you would have boarded at LBA....well just about!.....and better than been dropped off 16 miles out of town!
There has been a slow but sure demise of domestic air services in the UK over the past ten years (or more) and it aint finished yet! Sad but true!