Libs were originally not affected by BE because they also enhanced BE and created an infinite loop of interdependence. Labs eventually replaced libs and continued to not be affected by BE, presumably as an oversight as no such loop would occur. Guilds were changed so that wizard production wouldn't be affected on highly drafted provs that were idling around between war because it was the trend at the time to give warring kingdoms all kinds of crutches to minimize their downtime between conflicts.