Smaller body platforms might have been good with non-power front disc brakes, as most import cars were. The manual disc brakes cars might have been around, but probably not many, I suspect. I know what it takes to stop my '77 Camaro with power front disc brakes. I would not want to consider what it might be with non-power front disc brakes, although they were available.
My other gut suspicion is that IF a dealer ordered an A-body with non-power front disc brakes, for whatever reason, they didn't order any more of them.
Just some thoughts,
CBODY67