I agree about potatoes, but that only works for relatively cooler climates, i.e. places like Poland or Ireland. It can easily get to 35-37 degrees Celsius in the summer at the place where my parents live (not to mention places like the Indian subcontinent or Africa), at which point storing potatoes becomes a challenge.
> But it has so many times more meat on it than a chicken, and is more energy efficient per calorie consumed too.
It's all about the return on investment. Raising cows only becomes financially viable once you pass a certain number threshold (meaning big farms), otherwise you're pretty much doing voluntary work. It's a lot of work in order to feed a cow, I mean, lots and lots of work, and said work is pretty effective in burning calories. A lot of farmers in the European Union who are in the cow-raising business (I'd say most) wouldn't make it without financial help from the EU and from their governments.
I'd say that goats are a lot better option if you really need meat. They feed practically on everything (cows are a lot more picky) and they're smaller, so they're easier to "store" and protect at night. This is why I think they're so widespread in the poorer regions of the world.