IIRC throttles are legal in the US because of lobbying by Pedego as a way of overcoming disability and letting more people ride.
The problem I see is that many cheaply made bikes come with throttles, and many quality bike shop bikes don't. This means that many new riders (who think they need a throttle) never try riding a better bike.
When the cheap bikes break down, they just give up and leave it in the garage, and assume that all bikes are like that.
Not much that can be done about that since the big manufacturers aren't interested in adding throttles.
If a throttle was just a inexpensive upgrade, I'd add one, but buying a bike you don't really like only because it comes with a throttle is a mistake in my opinion.