Paul talks good sense, but there are other factors.
Sheffield's shopping areas stretched from Haymarket to the bottom of the The Moor, a very long shopping areas, where most other Cities had a much smaller defined area. Also when Meadowhall was being opened, to provide a much more compact shopping area, sheltered from the climatic elements and considerable free convenient parking, the Labour council of the day viewed the car as an enemy and put all their resources into creating virtually free bus services, while increasing car parking charges and one way systems, etc.
Is it any wonder that there was a mass exodus to Meadowhall, which was packed, while Sheffield City centre was virtually empty.
Now, of course, there is the added element of who has money to shop and currently Sheffield is not attractive enough to draw people into it to spend what little they have.
Hopefully the new developments will go some way to remedy that, if not what is the future, surely not just discount shops, fast food outlets, pawnshops, etc.