2016 jeep cherokee 4WD

This past weekend I drove off the side of the road and was hung up on the edge  of the road. My jeep was in "snow" mode.  When I tried to back out the front wheel on the drivers side (which was on ice) would spin, and the rear wheel on the passenger side would spin, (but because of the way the jeep was hungup , there was no weight on this rear passenger side wheel) and it would just spin.  The front wheel on the passenger side and rear wheel on the drivers side would not spin. Bottom line I needed to be towed out. Why wouldn't all 4 wheels have torque and spin to pull the vehicle out.