Why can't stepper motors be powered off of 9V batteries?
You can run stepper motors on 9V batteries. You just have to respect the batteries limitations:





Imgs from this datasheet.

Which means, a limited amount of current (typically 300mA max), at a low-ish voltage 4V~9V, during maybe 1~2 hours.

So it's not impossible, it just doesn't make much sense, thats all.