There might be some plastic or cardboard shims that you need to slide out of the slots in front of the copper wire before you can peel the copper out.
If the copper wire still doesn't want to come out then you might have to take a pair of wire cutters and snip the top of the copper on each side of the motor.
Then you should be able to take a pair of pliers and peel the copper wire out. It might take awhile to get it out but It should come out.
If it's too hard then you can just sell the electric motor for scrap.