Grass finished [if you want to call it finished] can never be any more then a small portion of the US domestic beef industry. I special interest market, an OK segment of the US beef industry.
Fact is, The US is the worlds largest importer of beef. All grinding grade beef except for the high quality fed beef that comes from Canada.
The reason we import so much? We simply don't have the cow numbers needed to supply one feeder calf per year to the US domestic beef supply.
The reason we don't have the cow numbers? We don't have the forage. Summer grazing and stockpiled.
The US does have the ability to feed more cattle. [corn, soybean and other feeds].
For instance, the US will buy all the feeder cattle Mexico and Canada can supply. All will go into feedlots.
The Northern States and Canada Are on stockpiled feed [hay] at this time or soon will be. This hay is mostly to Winter the cow herds and replacements. The only way this works for the US beef producers is to put feeders on grain in feedlots or on grain at home.
Simply is not practical to try get the desired weight and quality from feeding forage only. Even if it were available.