That is, admittedly, a lot higher than I was expecting! But 70% is still a sizeable majority. Moving the entire industry to grassland feeding would likely result in a fundamental upwards shift in how beef is priced, one that I suspect the GP would be unwilling to accept.
For every other meat type, it's overwhelmingly factory farmed (98%+).
0: https://www.sentienceinstitute.org/us-factory-farming-estima...