Yet another example of the complete shambles that we are now stuck with following the "Privatisation" of British Rail. Not only has it been fractured all over the place, with pages of 'agreements' replacing 'someone actually doing the work as it is needed'. I don't see the old BR through 'Rose coloured glasses', I used to work for them for many years, but when it was destryed by the Major Governement, they were actually doing very well and things were looking up.
The simple thing would be which TOC used the station most, then that TOC should be responsable for it, but that is practical, simple and common sense, but for those reasons alone it wont happen.