They are popular for cargo bikes; picture a parent with a couple of kids, or a big grocery run. They are also a great way of commuting without having to worry about being sweaty when you arrive, if you have a long commute. Lastly, they are great for people who are getting back in shape or starting to suffer the effects of aging. They are great all around.
The point of pedal-assisted e-bicycles is to assist pedalling and they are hugely popular. Around 30% of bikes I met on my ride today was them. It's a hilly ride with some slopes that are way too steep for recreational cyclists, older folks and children; this way they too can enjoy nature further away from the city.