Because it's a main source of active power that can be re-directed.
A battery on an EV can be too, in which case the main contactor should be verified disconnected prior to any software update. But typically people don't refer to that as the 'engine'.
So prime mover encompasses engines and main batteries.
A ton of cheating can be stopped dead in it's tracks if you spend some time filtering out data being sent to the clients, that have no business knowing about.
Where I could spend a few hours(training) to get the NIA to work, it all goes out the window the moment you move it or take it off.
So the solution is to permanently implant the electrodes into the brain. (Even on the scalp will move over time, so that's not an option)
But the issue with implants is infection and scar tissue formation.
They haven't been able to solve the infection and scar tissue problem all these years, and Musk isnt' doing any better with it. Even with nano wires.
Even Valve has been working on Brain-Computer interface for years.
IMO, they should give up on the permanent fixation, and look for some kind of reference point, and do a antenna re-alignment that can be calibrated every time you put it on.