because if a mage were trying to attack with magic and they started running up afterwards that would mess them up. Also because in close range I wait until the moment my enemy attacks to throw a spell so that way it won't be interupted.
Also, you can solve this problem by double clicking the mob, THEN using skills, at least that always worked for me. It doesn't work well with skills like Stinger though, so use that, double click, and then use skills.
Was I of only help to you? If so, please give me karma! Kthx.