FWIW< I live in an area where market gunning flourished.
I've seen the tally sheets and price lists for the sale of harvested game. I don't think it was a big money maker.
Other opportunities (at least in this region) reduced/eliminated it's necessity.
I'm sure there was always a market for fresh shot game, but I think by 1920, the shipping of barrels full of salted/iced canvasbacks, was in the rear view mirror.
When I hunt my local marsh, I remember the earlier writings of a man that shot canvasbacks and rails on the very fields I see as having been diked and drained for food production. By 1930, cooperative flood control was in full swing.
No more celery beds at the end of my road.
