If the farms in question were further from the city, better farmers would buy/rent them and the land would be productive again.
1. You are assuming "better farms" have the capital and will available to purchase the land.
2. Just because a competent farmer purchases the land does not make the land arable. It could take decades to undo the damage from improperly cared for land.
I am assuming a functioning market for farmland. As I have observed over several decades, and my father and grandfather observed for much longer, the market for farmland is brutally efficient. (Insufficiently-regulated monopsonies arrange society so that their inputs are as cheap as possible.) Lots of rural land lies fallow, and much of that has ruined some poor farmer who tried to grow or graze ground that wouldn't pay him back. My point is just that while we can draw that conclusion about empty fallow ground, we can't draw it about ground that currently sees more remunerative use than farming.
I don't think we can really know anything for sure about point 2 for hypothetical internet discussion agricultural ground. It is probably true that some land has been so damaged, but it is also possible for farmer B to have better results than farmer A on the same land. This is possible even if they are in some sense equally skilled and capitalized. It doesn't rain the same every year...
When someone wants to sell a field the real estate agent will ask for copies of the forms you submitted for government insurance, and other forms of proof of that it yielded. you don't have to give this, but it is a red flag to most farmers (not all farms collect this data, they are not worth as much). Giving incorrect information is fraud.
Of course there is always information asymmetry, but farm buyers are aware of it. In most cases the buyer already lives in the area, so they know just be driving by over the years what really happens.
He may also just be working the land of let's say Bill gates and not care much for it's longterm potential. I feel like a lot of us in this thread are just throwing guesses out there.
1. You are assuming "better farms" have the capital and will available to purchase the land.
2. Just because a competent farmer purchases the land does not make the land arable. It could take decades to undo the damage from improperly cared for land.