Can't imagine why ATC don't use them more often.
All respect, but it's not actually up to ATC to issue/use them.(Except when using them as a separation tool under radar control.) We are required to follow our procedures; nothing in those procedures,
AFAIK, suggests we "suggest" to aircrew on opposite GPS tracks that an offset right is a good idea. The presumption being that such flights shall always be separated by the appropriate vertical spacing. Fortunately, in the vast majority of cases, they are.
I've spoken with pilots who consistently report accuracy of a wingspan or less on GPS routes, as was tragically demonstrated by the collisions referred to above.
I totally support the idea of an offset being introduced in these cases, where it doesn't invalidate the airway separation being applied. Can't see how it would, in most cases.
It will, I think, fall to pilot's unions to make this one happen. Keep lobbying.