I think there are multiple reasons to use a motor and multiple ways to do so. Some of us just want it once in a while (I use it to boldly go where I haven't gone before...rides that include big hills I would not attempt unmotored). Some of us want to get where we are going faster, and use it as transport, not intentional exercise. Some of us have health issues so it allows us to keep riding beyond our bodily limits. Some of us don't want a motorcycle but want the speed on a bike without the hassle of registration and insurance.
I chose a tiny battery because I knew I would not be using it very much. If my needs change, there are larger (heavier) batteries I can purchase. But for now, riding analog gives me pleasure and exercise but the motor gives me the confidence to branch out further than I otherwise would on a ride.