Basically, the Copenhagen Wheel moved all the complexity of setting up a hub motor drive system - motor, battery, controller, sensors, computer - into the hub shell itself.

Which made it seem neat and clean, but meant it had serious reliability issues, couldn't handle wet conditions[], wasn't really repairable, and was expensive compared to more reliable alternatives with better battery life, etc.

[] The manufacturer apparently stated that "[...bad bearings] can occur when the Wheel is repeatedly exposed to wet conditions. Due to the nature of the problem, this cannot be repaired": https://forums.electricbikereview.com/threads/known-issues-p...