I've had the discussion with them twice. For leveled spells they're trying to conserve, but to a ridiculous extent. Like fully rested before a known dragon encounter that is also an explicitly stated last encounter of the dungeon and reminded to use spells immediately prior to the encounter and never used a leveled spell. But they never give an explanation for not using cantrips beyond "I just forget". This is when we have the discussion about "well it seems like the mechanics of this class are really at-odds with the way you like to play, maybe next time you should try a Paladin?" Which seems to go over well, until the next character sheet shows up in my inbox.