As noted above they do turn. I think it would be potentially dangerous to allow a software change to prevent the wheel from turning the tires, so unlikely to be implemented.
I understand that, but also, the tesla has software configuration for e.g. how tight the steering is, so ostensibly it would be possible. But it does make sense that there would be no way for the steering column ECU's CAN messages to be blocked from reaching the steering ECU.
