Towing with the rear lifted and the front wheels on the ground wouldn't result in the drive motor spinning and generating electricity without active cooling or the control of how much electricity is being generated, etc. I don't understand why this is discouraged other than the steering wheel has no steering lock so would be free to turn side to side which might make towing tricky and possibly dangerous. However, tow truck drivers probably have a way to lock the steering wheel in the straight ahead position so that it couldn't turn side to side.
[Bought 25 April 2022] 2019 BMW i3 Imperial Blue Metallic, Giga World, Tech + Driving Assist, Heat Pump, 428 Wheels
[Sold 15 June 2022] 2014 BMW i3 Arravani Grey, Giga World, Tech + Driving Assist, Parking Assist, DC Fast Charging