It's more simple than that even, grains are simply more portable and last longer. Those two properties are the major reasons they are the staples of our diets.

It's more simple than that even, grains are simply more portable and last longer. Those two properties are the major reasons they are the staples of our diets. There's little sense in growing and processing them on site at food distribution centers. Growing and storing them within a reasonable distance of food distribution facilities is sufficient for sustainable reliance on grains. I believe rice can be stored safely for years given the right conditions. There are no sustainable conditions under which leafy greens can be stored for as long as rice.