It was as if they had practiced the act of running for their lives before the battle. They escaped as soon as someone moved in their direction with a group after looking at them with bad intentions.
The morale of the villains was high. Plus they couldn't surrender because they were afraid of being killed later. They were not heroes who could surrender and would only suffer some harsh words. Any villain who surrendered was sure to die after the battle.
Plus, there were a lot of financial rewards waiting for them regardless of the outcome of the battle. The villains would be rewarded based on how many enemies they kill, not based on the victory of the villains as a whole.
The fact that they would gain double the reward and a lot of popularity if they won is only the uncertain dessert after the meal. The villains cared about securing a good meal. So they fought with all their might.