If you really need it, the "logical reason" is that they spend those action points to do minor first aid on themselves, bandage themselves up. If not a talent, it could be a Personality Trait -
Battlefield Medic - "You've spent so much time fighting that you are experienced at using anything on hand to patch up small wounds, but all the time in battle has made you unable to fully rest in peacetime." (Convert up to 2 unused AP for in-battle healing, but resting in a bed only heals you up to a maximum of 80% of your max HP.)
I only include that downside because I was under the impression that Personality Traits have a mix of bonuses and downsides.
