Is it possible that a lot of the current GA airfields from the Southeast all the way up the east coast as far as Aberdeen were former RAF fields hurriedly built in the early 40,s because they were "Hitler facing" rendering any potential airfields sites in the west less desirable from an operational and geographical standpoint, particularly in the Northwest?
There were very many wartime airfields west of the pennines, too, for training, defence, and aircraft production. So many in Shropshire that often their circuits overlapped! To list them would take a book (and it indeed has - a whole volume of 'Action Stations'). Some north of Shropshire that are or were still around and one might have thought would survive include Calveley, Cranage, Stretton, Burtonwood, Woodford, Burscough, and Mier.
I suspect the massive growth of Manchester Airport and its all-enveloping control zone explains some of that, but not all.