What causes a carrier bearing to push out?

The rear section of the driveshaft has a slip yoke in it. This allows the rear section of the driveshaft to change length as the rear axle moves up and down. If this slip yoke binds, the change in length is absorbed by the slip yoke at the back of the transmission. Because the carrier bearing itself is fixed to the driveshaft, and the hanger that holds the bearing is fixed to the frame or cross member, when the rear slip yoke binds, it moves the entire driveshaft forward taking the carrier bearing with it, and pushing it out of the rubber in the hanger.