Yes there were a lot of aeroplanes of all shapes and sizes using Sheffield for a very short period of time, the trouble is that there weren't enough passengers to make any of the routes viable.
Put an airport next to a motorway, within easy reach of national rail links, only 1 hours drive from Humberside and Leeds and try and operate similar routes with more expensive fares - I wonder why it wasn't a success?
Having been involved in it's operation for a while, I know that it rapidly became a very expensive white elephant and no one in their right mind would have taken it on as a commercial enterprise after all the scheduled routes failed.
It doesn't take a genius to work out that Peel only took it on because it helped smooth the political path for the development of Robin Hood - a fact they've never denied.
It would be great if Sheffield could remain available as a G/A facility, but who would pay the bills?
Come up with an answer to that, and you'll probably find that it will stay open.