Vertical Schfarms

I'm listening right now to a podcast with an author nattering on and on about the future of vertical farms, which essentially means indoor hydroponic farms that feed urban populations without requiring all the soil and acreage of traditional land-based agriculture. It's a compelling sci-fi sort of concept, especially when you hear that currently to feed the city of New York it takes the land acreage of the entire state of Virginia but, according to vertical farm theorists, at least, it would take only a thirty story building on a single city block to prove the same number of calories.

All well and good, except for one thing. I'm not aware right now of there being a particular shortage of farmland in the United States. It's not like farms are bloating out all over the country and starting to gobble up the land that used to be used for subdivisions. Instead, in my neck of the woods, at least, huge tracts of lands that used the be used for food farming are now being planted over with pine trees for timber and leased out to groups of town-dwellers as hunting land. (As is the case with the 800 acres of former farmland my family owns in south Georgia.)

So what problem, exactly, are our "vertical farm" advocates trying to solve?