Bad electrical connections can result in sufficient resistance in the connection that will result in an electrical load without the motor turning.
Damage caused by body shops (one bunch literally chopped through the cables in my quattro to replace a door, and used badly crimped bullet crimps.)
Badly reconnected connectors- some multipin connectors have moisture seals which make pushing the connectors together difficult. Some have removed the seal, thus allowing moisture and corrosion on the pins. Simple Verdigris affecting the connections.
Motor jammed? Again, moisture could affect the internals of the motor. It's far from unheard of, and may simply require opening the motor case, cleaning it all up/servicing.
Cable spool/pulley damaged/cable jumped? The system works on a cable being wound around a loop. There is what looks like a plastic spider as part of the 'gearbox' attached to the motor. The spider can crack with age, causing the mechanism to bind when the motor applies tension.
If you have evidence of an electrical load, then it really is worth looking at the mechanism more closely before abandoning it.
A little pic-
