The trick with hunter-gatherers is that they simultaneously lived pretty relaxed lives, and about two days from starvation. The key point is accumulation: hunter-gatherers didn't have a way to store or transport food in significant quantities, or much of anything else either. They didn't work much harder than they had to because there wasn't much point, but they had to keep at it; a good hunt keeps you comfortably fed for a couple of days, but then the meat spoiled and you had to start all over again.
Some combination of pride and testosterone, I suppose, on both sides. War was a masculine business, and it's always been hard to convince people who were lately slaughtering each other that they're all friends now. Women tended to keep at arm's length from conflict, so reconciliation becomes easier.