When you change the tone of your campaign from generic fantasy to something else there’s always an adjustment period. I tried to run a few superhero games over the years, and the characters have always had more in common with Spawn, Venom, or the Punisher than a traditional superhero. Murder was pretty much the default assumption, and the acquisition of loot a major driving force.

Plus, there’s the fact most super hero games are level-neutral. You don’t gain new abilities or talents. Getting past the desire for loot and levelling up a character is probably the hardest element of switching to more narrative or less level-based systems. The players are so used to regular rewards and power-ups. This might drive them to familiar behaviour and reactions as a form of comfort.