Just so I am clear, my concern comes from observation of the farms I work. All the usual caveats of anecdotes apply. It is not something that I have formally studied.

With that said, I think fertilizer is a big part of it. While we always used some synthetic fertilizer in my lifetime, the needs are greater now. Another thought is a greater opportunity to diversify the crops grown in the rotation. Things that humans can't eat, but animals can. There seems to be a difference in growing food for people for a few years and then growing food for animals for a few years over trying to grow food for people every year, where the choices are much more limited.

But this is speculation on my part.