Basically, as I said before, the management at MAN cocked up by not embracing the low cost era at the start.
There's nothing wrong with airports competeing but too many airports in too small an area just dilutes the mix and reduces the viability of the airports and the services they offer.
There was a joke about Ryanair serving the five Manchester airports:
Central (Manchester), West (Liverpool), Northwest (Blackpool), Northeast (Leeds), East (Robin Hood)
That's fine for an LCC developing new custom but for all those airports to aspire to serve a range of short, medium and long haul routes doesn't make sense.
You don't get people in Hampshire expecting a vast range of services from Southampton, or people in kent expecting Manston to be a major hub - they go to Heathrow or, to a lesser extent Gatwick.
Long haul from Luton and Stansted has never consistently worked and for an airport to develop it needs to attract a wide range of carriers and routes and provide the ground based infrastructure to handle volumes of aircraft, passengers, cargo and ancillary services - something only Manchester is physically capable of in the North of England.
Historically, Manchester has had to fight the problems of BEA/BOAC/BA interference in its bid for routes, yet it continued to grow until the current malaise (howsoever caused).
Even with excellent competing rail services it has maintained healthy figures on London services whereas Liverpool, since the demise of British Eagle, has never sustained a London service, even at the level of one return a day. Leeds is now going the same way. Unless I was interlining at Heathrow (God forbid!) there's no way I'd take the plane from anywhere in the Liverpool to Hull corridor to London but I'd be happy to use the excellent train connections to Manchester to fly elsewhere - even using the motorways outside peak periods.
Many years ago I was responsible for marketing what was then the GMC to business tourism. As such I sat on various committees belonging to Tourist Boards, Chambers of Commerce, Local Authorities and Manchester Airport. It was agreed by a wide spectrum of both business leaders and politicians on the west side of the Pennines that a single major airport needed to be backed and developed to attract direct air services to/from the region.
That was back in the early 1980s. From the end of that decade until the late 1990s Manchester achieved the aims set out ten years before.
Since then - and not helped by 9/11 (although Manchester seemed to suffer less in the immediate aftermath) - the story looks to have been one of missed opportunities, mismanagement and a lack of foresight and flexibility.