I know there's been speculation on here that this was the case. Nothing definitive, because internet. But this "tuning" company figured it out:
Ghost Upgrade - Why is it restricted to the 1120980 rear motor?
The power electronics are superior in the 1120980 motor. Model 3 Performance models all have this motor number. The 1120990 motor is less powerful so it’s impossible to increase the power by 150HP. The Boost 50 module is the maximum power for this engine.
Ghost Upgrade
Ghost Upgrade - Why is it restricted to the 1120980 rear motor?
The power electronics are superior in the 1120980 motor. Model 3 Performance models all have this motor number. The 1120990 motor is less powerful so it’s impossible to increase the power by 150HP. The Boost 50 module is the maximum power for this engine.
Ghost Upgrade