We absolutely should cover those, but there is a lot of farmland. There may not be enough "mall-land"
If the economic benefits of adding solar to their farm outweighs the costs then farmers will start adding them to farms.
It’s also fascinating how quickly the Nirvana fallacy shows up when it’s time to talk about renewables. Supposedly chopping down forests for solar (which isn’t the main way of getting land) or the farmers choosing to put something on their land is top of mind. But chop those forests to make something else, or have the farmers grow super subsidized corn and there isn’t a peep.