Let me take you back to the 1970s, when electric bikes like we have now were about as feasible for personal transport as jetpacks. Raleigh's most popular bike by some margin was the Twenty, a bike with 20" wheels.
Enthusiasts who rode lightweights scoffed at them. Small, fat 1 3/8" wheels? How could anyone use something so inefficient? And no suspension! It was considered by most enthusiasts to be a really terrible bike. But it wasn't!
They outsold lightweights because to non-cyclists they were reliable, unpretentious transport. You didn't need special clothes, or to belong to a club. Lots of room for your shopping, easy for more than one person to use (you can adjust saddle and bars without tools), they take up less space, and they're cheaper than shoe leather.
The sort of person who bought a Twenty 50 years ago chooses a bike like this today. They don't give a stuff about efficiency, they just want to get to work. Yes, the motor does do much of the work, but what's wrong with that? You are talking about efficiency and it's true - a 175w cyclist would not be able to ride one of these fast without a motor so yes, by your definition they aren't as efficient as a "proper" bike. But a 250w motor makes the resistance of the tyres and the weight of the bike irrelevant.
There are LOADS of good engineering reasons to design a town bike like this:
- Small wheels give a low centre of gravity for load carrying.
- The design of the frame makes for a bike that takes up less space - important if you live in a small space.
- The step-through design makes for more confident mounting and dismounting, and the
- Small wheels are inherently stronger than big wheels. That's important, as hub motors stress wheels in ways human powered wheels aren't.
- Big tyres at low pressure are less prone to punctures.
- Big tyres at low pressure soak up potholes. You will not pancake one of these wheels going into a pothole, like you can with a 23mm road bike wheel. It's a much more practical solution than the suspension a bike of this type with skinnier tyres usually has.
That there are couriers riding bikes that look superficially like these but are illegal is a different question. Let's establish that it is possible to build either of the bikes you've posted photos of with completely legal pedelec motors. I have a friend with a RadRunner - that's completely legal, with 20x4.0 tyres and a 250w hub motor. It's fun and practical personal transport.
TL; DR; A vehicle that goes up to 15.5mph with human input and a 250w motor is far more efficient than a 2000kg car with a 37500w engine and a top speed of 200mph without any human input when you're talking about getting a single adult from point a to point b in a town centre. That's probably the comparison you should look at.