You are missing nothing! A DC electric motor will draw maximum amps at start up, and then reduce to very little when up to speed. It might be the case that even with the drive train attached the amp draw differs little from the free-running amp draw.
From your description I would be looking at the motor first. Check it looking for faulty bearings and burnt windings. If you can free the bearing up do so, but if the windings look burnt you're cooked. My other suggestions are that one of the rotor sensors may have gone down so it isn't seeing the rotor and the firing sequence for the coils has gone awry or that the sensor wire is faulty. Both of these assume it is a sensored motor!
Now you know you are not going mad, I hope you track the problem down.
