Comment by freehorse

On the other hand, a motor you can strap can also be unstrapped, and then you can use the bike as a normal bike. When you have an electric bike, it is usually too heavy to work comfortable without battery (ime).

I am not sure if this is enough argument for having this instead of having a decent electric bike plus a normal bike, but it is an argument I guess.

There are cases one may not want to use an electric bike, eg when going out for a coffee, a drink etc and you may not want to carry the battery or risk theft, in contrast eg to biking for 40 minutes every day for work each way.