It looks like leadership exp is only gained when you have used a physical attack (melee, ranged, or magic missile) within the past x minutes, to prevent people from AFK exping. But it looks like mage spell attacks aren't counting towards resetting that timer, so if you're a mage using exclusively spells to attack, you won't get any leadership exp from your followers attacking stuff. You have to remember to use your wand to stab a mob every few minutes to reset the timer to continue getting leadership exp.
It looks like leadership exp is only gained when you have used a physical attack (melee, ranged, or magic missile) within the past x minutes, to prevent people from AFK exping. But it looks like mage spell attacks aren't counting towards resetting that timer, so if you're a mage using exclusively spells to attack, you won't get any leadership exp from your followers attacking stuff. You have to remember to use your wand to stab a mob every few minutes to reset the timer to continue getting leadership exp.