Meat is made, inefficiently, true, from grass. Where grass grows, it is generally so because nothing else will grow there. So in a lot of places you can't swap

Meat is made, inefficiently, true, from grass. Where grass grows, it is generally so because nothing else will grow there. So in a lot of places you can't swap out meat for, say, corn. It's meat ... or nothing (well, grass, which I guess you could make plastic from but little else). All of agriculture is also pretty inefficient btw. From the sunlight to calories (before any processing) there's ~1.8% efficiency.