Slash and burn is ancient agriculture, too. While Wikipedia calls it sustainable, it was only sustainable with approximately no humans, resulting in functionally unlimited land. Larger populations can't wait for the forest regrowth part of the cycle.

/grandiose We are genetically programmed to live for a few decades, reproduce, and care for our kin (both blood and tribe) in a world which was limitless (relative to us as individuals.) I deeply fear this is the sad answer to the Fermi paradox. Now, our survival depends on outsmarting our short-sighted genes.