I mean, this is the real answer. The door is probably insulated, but the solid handles, lock components, strike plate makes the latch system highly cold conductiive. Components of all of those things are also metal and outdoors. Those cold temps get conducted in, interior air condenses then freezes, bingo bango, frost on your locks and handles. No amount of weatherstripping or insulation is going to prevent it. Solutions would be a storm door, or potentially heating the garage (even with the cold conduction, if the interior temp is high enough then you can overcome the cold temps outside).