"Without any external pressure, multiple peoples concluded that settling and eating grass was preferable to being nomads."

Portraying it as an individual choice is inaccurate. The process of populations becoming sedentary(and agrarian) spans over multiple generations and wasn't really reversible. The early settlements likely only worked because they had some method to force people from leaving and the later settlements had to be sedentary because their neighbours were sedentary, it had a cascade effect. Oversimplified but that's the gist.