Once the freewheel body butts up against the shoulder/stop on the hub, no further rotation is possible. The torque on the cogs ends up pushing the body laterally against the threads. It's like kicking a door-stop wedge under a closed door, once it stops moving, you can kick it as hard as you want, it's not moving until the door breaks. It's not the friction of the wedge on the ground that stops it (such as when the door is open), but the strength of the wedge and door materials. Compute the entire contact surface-area of the two thread-faces and multiply by the modulus of aluminium and you'd need a tremendous amount of torque on freewheel-body to strip the threads. Beyond what a human can generate.

In this case, it's most likely due to either mismatched French/English threading or the hub-threads were previously damaged from cross-threading.