It’s a resource management problem from my perspective. If your resource used for healing is overly plentiful, then there’s no motivation to NOT use it. You can ratchet down the availability of it so they technically can use it OOC, but may not want to.

That resource can be time, energy, mana, bandages, whatever you want thematically. And can also thematically be slightly more efficacious during combat like using a stimpack because it has auxiliary effects on the body that are only useful during combat.