well the thing is for hunter gatherers, they simply didn't need to, and the attempt to do it would have hurt them. being hunter gatherers gave them plenty, but couldn't support static population centers like what agriculture helps provide, and the stockpiles of food that the agricultural city people had was where language came from, to keep track of it all. Hunter gatherers were just as capable as those in rich river valleys who would settle down & develop agricultural societies after the ice age, but it wasn't advantageous.