The thing is, the switch from ATCO to non-ATCO often doesn't save that much money as an on cost.
Most office-bound ATCO jobs when they get converted to non-ATCO tend to get converted to T&S B or C grade posts which, although are paid a bit less than top-of-the-band Band 5 ATCO 2s, are paid as much as many long-serving ATCO 3s out there.
The big benefit comes from getting the sunk cost of the trained ATCO back in the Ops room. That's if they validate...