Same reason we don't have them in Drawer Box Designer. We can't use the same v## variables as cabinets because as soon as a door or drawer goes on it could pick up a cabinet variable. So the thought came of a different variable for doors and drawers. Then there becomes the issue of two different doors or drawers that have different values for the variables, how can they maintain being separate but still exist. Then how do go about updating them in Constraint Manager. Lots and lots of layers to it. Not saying it isn't possible, it just wasn't possible in the time frame of adding Part Editor cuts to doors.