USDA defines a farm as an operation that produced and sold, or normally would have sold...
Are we talking about farmland that had been sitting dormant for years collecting govt subsidies? The ostensible reasons are for: prevent farmers from growing too much food (don't let food prices get too low), or Conservation Reserve Program (fight erosion and such), or now to fight warmageddon?
To get those subsidies you had to "prove" that you would grow food even if you weren't going to really. It may be that some of the farmland "lost" is people making money with it other ways like building houses and such. In other words, I want to know how much of farm land was lost of land that was really used for farming.
As a former farmer, I would say the most likely scenario is a farmer was ready to retire and there was no one in his family who wanted to take over and so they sold out to developers.
“Would have” may mean a farmer stored his crop one season to be sold in another, or one’s normal crop was diminished by drought, unusually low prices, or other disaster.