The real reason they first spring to mind as the replacement for livestock is western vegan cultural chauvinism.

Aren't beans and similar plants even more prominent in the global south, with what sort is most prominent depending on the local climate? It's mostly in American cooking that they're rare or reduced to some revolting, poorly cooked side dish.

That said I can't imagine there's anywhere they take on a similar prominence as meat has in the American diet, they're just a common addition to food because what they bring to a dish is generally good.