In addition to the other reasons given, it’s possible that the gearbox wouldn’t hold up with the new motor. Tesla originally built the Roadster with a two-speed

In addition to the other reasons given, it’s possible that the gearbox wouldn’t hold up with the new motor. Tesla originally built the Roadster with a two-speed transmission but the high torque of the electric motor kept shredding them, and they finally shipped the car with a single fixed gear ratio. I think there are a couple of super high end EV models with transmissions, but almost all EVs just have a fixed ratio.