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.
I kinda read your suggestion wrong. I was myself suggesting (and asking if it is already in in some form - still asking if Sven or someone else happens to read this) for a feature that is constant and nonupgradeable, and somehow related your suggestion to that line of thinking aswell (even though you did say, you copypasted it from "talents" thread).
Yeah, yours could make a nice "trait/talent" for higher level characters. I know there are a bunch of people who would likely consider it a "health regen - run few steps away from enemies, heal for the remaining AP, rinse and repeat until full, win" but I think that sort of thing could be mitigated somehow (use only every X turns, for example)
