1) I'm sure you know, but "grass-fed" does not mean "grass-finished".
Most of those "grass fed" farms still do a final bulk with corn (which, honestly, defeats the whole point of "grass-fed"). The monetary incentive to bulk on corn is simply massive (the animal winds up like 3x the weight).
2) The biggest problem for boutique farming (like "grass-finished") is the lack of consistent order volume.
The big farms amortize the price of feed, the price of butchering, etc. over a consistent and continual number of cows. Boutique farms suffer all these and gain none of the scaling.
I have tried to get my local "grass finished" to start marketing to all the "Froofy Diet Types" (for example: Gundry Anti-Lectin which is anti-Corn) which would dramatically increase their volume. Unfortunately, the political overlap between those who produce grass-fed cows and those who consume "Froofy Diets" tends to be a null set--creating a set of attendant problems.