Some of these machines are listing capacities of 300 pounds of cargo in addition to rider and 70 pound weight of bike. That's well in excess of 500 pounds.
I am going to purchase a Yuba Mundo Lux which is the Version 5. It has a cargo payload of 200kg. This is 440lbs. I doubt that I will ever load it up with that much weight. I am going to put a Heinzmann cargo bike motor on it. I will put the front hub version on it. I need the torque not the speed. It puts out 600watts and 111 max torque. at 25km. Hardened steel gears in an oil bath. GVW of around 700lbs.
It's actually the other way around; they were banned before they existed; the actual issue is that they've never met the safety equipment requirements for registration as motor vehicles, though they clearly are (and have been interpreted to be such), therefore they are illegal - not as "e-bikes" (though of course that is the wording popularly used), but rather as unregistered electric motorcycles.
From reading some blogs I believed that they were banning any kind of bicycle with an electric assist. Some of these so called advocates are one sided in the stories they tell. I believe an ebike should be as useful as a regular bicycle. It does not need to be powered at 40 plus mph. People have no business on a public path being dangerous. The root of the problem on these MUPs is people who do not care until there is calamity.