They're too expensive right now.
Building a good one (gotta build because otherwise they're speed limited and even more expensive) would cost me a couple thousand dollars. My 1100cc motorcycle was cheaper, and it'll do 0-60 in under 4 seconds and tops out at nearly 150.
And they don't really work for most of my use case anyway, if I'm going to the grocery I'm getting more than I'd feel comfortable carrying on a bike. It makes more sense for me to use the plug-in hybrid car, uses no gas and much easier to transport the groceries. Now, it might make sense when I've got a client downtown if purchase cost was cheaper, it's easier to park a bicycle than a car or motorcycle. But free bicycle parking for a couple thousand dollar e-bike vs parking fees I can bill to the client isn't great, and anywhere but downtown and I'm still gonna have to take the car.
If it wasn't so hilly here I'd probably use the regular bicycle more. But I don't do uphill and I'm not 25 any more, I don't think I could beat cars off the line and treat the speed limit as a minimum like I did in grad school.