Supervisors have too many other duties on their plate nowadays, it dilutes their radar skills and takes away their attention from what should be their primary function.
In the Area centres, I believe that suitable ATCOS should be asked if they wished to become active as a GS/LAS. If they say yes, they would receive half a pay spine.
There would then be a large pool of ATCOS who could be rostered to carry out the function. It would result in current ATCOS doing the GS/LAS role 2 or 3 times a month and remaining very valid on radar