Just because you noticed "Hey, this unpopular grain grows so easily it's popping up from the sidewalk!" does not mean you can actually then go and scale that to providing food for hundreds of millions of people.
We developed modern agriculture the way we did for a reason. Some of those reasons are no longer valid, true, but a whole lot of them are still very very pertinent.
I think vertical farming / rooftop farms / etc are at this point largely an exercise in virtue signaling more than they are actually improving the food system. They might be improving it for high-income Whole Foods types who are upset Amazon owns their favorite store now (ie: us here on HN) - but those people aren't exactly the ones who need to see improvement.