I think there's a triumph of marketing in there. The Reese and Mullers of this world seem like they would be effortless consumer items that would somehow solve all your problems.There must be something about either the bikes or the buyers that causes them not to want to keep them.
Except you still get wet, and you're exposed to the world in a different way and you're going to get dirty. It is still easier to take the car, and if you make sure your recycling is properly separated then you're still doing your bit!
Compare that to the buyers of DIY ebikes. Most of the want to get to work, or use them to deliver things. They don't care how it looks so long as it works!
It's far more profitable to sell to Reese and Muller types.