It kinda is. The FDA regulates food and drugs - the FTC does the same thing for unhealthy market configurations. You can claim up and down that other options exist in both cases ("don't want to eat rat feces? buy something else!") but the regulation of unhealthy practices overall improves the quality of market options while also making businesses (rightfully) fear exploiting their customers.
In this instance, it's not like John Deere is using their position to improve the status quo of their product for everyone involved. They are explicitly demanding money for nothing - not only is it anticompetitive, but it's not promoting healthy market development. Deliberately designing malnutritional formula is really not that different from deliberately designing a tractor it's owners can't own. The mechanism for regulating both issues is pretty similar as well.
In this instance, it's not like John Deere is using their position to improve the status quo of their product for everyone involved. They are explicitly demanding money for nothing - not only is it anticompetitive, but it's not promoting healthy market development. Deliberately designing malnutritional formula is really not that different from deliberately designing a tractor it's owners can't own. The mechanism for regulating both issues is pretty similar as well.