toucanbuzz
No rule is inviolate
This quote caught my attention. If you read @GMforPowergamers's post, his DM conditioned players to focus fire by ensuring that enemies didn't surrender/flee even when critically damaged. There was no benefit "spreading the love" of damage."You taught me that wasn't worth it"
So, what about greater use of morale?
D&D provides loose guidance for morale whereas in AD&D it was very mechanical. An enemy might break ranks on taking its very first hit! There was a great incentive in AD&D to tag foes with damage because you were likely to trigger a morale check. D&D leaves it up to the DM, but I can very well see DMs conditioning themselves to encourage focus fire by having combats go to the death.
Yet, not everyone or thing wants to fight to the death. Beasts especially adhere to this. Not every soldier or bandit is a fanatic. Once the ambush fails and the bandits are subject to real harm, why would they fight to the death? Flee and live to fight another day is likely the motto of a robber.