The problem with being a sedentary farmer is that once you get your seeds in the ground you now have a long standing commitment to care for that plot of land. Folks don't really know now daysnowadays because all our food comes from the grocery store, but pre-industrial farming ain't easy. Its 12 hour work days 7 days a week for months on end, followed by a frenzy of panicked activity. This burst of frenetic labor will hopefully result in a harvest, weather, pests, crop choice, soil chemistry, and water availability permitting. If just one of those variables goes wrong guess what? You better be ready to heavily reduce or quit that whole eating habit until next year. Contrary to popular belief, people did not always experience famines in the dead of winter unless that year was REALLY bad. They starved in the summer because that's the period farthest from the last harvest. Imagine the maddening feeling of starving to death while luxurious green lush plants that aren't bearing fruit yet are growing from the soil. Pre-industrial farming was not fun. It was a ton of work, sometimes for little to no return on investment.
The other problem in a situation where social cohesion has broken down is that you are stuck defending that plot of land. Those lush green crops coming in perfectly (thanks in no small part to your and your entire clan or tribe's slavish back breaking labor) are a huge billboard that says "You could probably pillage the crap out of us." So on top of the grueling labor you also need to figure out how to defend a vary large plot of land. In summary, the reasons why farming sucks are back breaking labor, predatory neighbors, and no guarantee that you will even get fed once itsit's all done. Last but not least, if things don't go your way you are stuck there suffering through it. You cannot just pack up an entire farm and move it to some placesomeplace where conditions are better and attackers are farther away, right?
Or could you....?