A goodly sector of the community are allergic or sensitive to nuts, including me, so nut based nutrition isn't an option.
The other point of course is that if everyone became vegan, the figures would change dramatically. At present a tiny vegan minority is catered for without problems, but everyone moving to a plant based diet would soon engender the problems caused by a meat and fish based diet. As it is, rice paddies generate a lot of methane.
I suppose I should say that I find vegan living a bit odd.