This seems like a no brainer-- of course it's cheaper to use inputs from freely available outdoor sources rather than metered and/or artificially provided ones.

This seems like a no brainer-- of course it's cheaper to use inputs from freely available outdoor sources rather than metered and/or artificially provided ones. Since these plants evolved in that setting, it works rather well for them. There are still many important reasons to pursue indoor farming. For one, population dense areas have few other options, especially in a crisis. Perhaps more importantly, space travel, colonizing other moons & planets, or even the radiation-proof underground cities we may need right here on Earth would all depend exclusively on such technology.