For me my bicycles are utility vehicles. I commute by bike and run most my errands by bike. 2K to 2.5K+ per year. But I am not really interested in cycling for just sport reasons. Yes I love the exercise as long as I can combine it with some usefulness. No matter if it is getting to work, the groceries, a few beers at the next pub or just plain sight seeing. Yes I love cruising the trails here on my recumbent and just enjoy nature.
When I was in Germany a few weeks ago I rode my late dad's ebike my mom still keeps for visitors. I really liked it. Especially the support of the motor when going up hills. I have arthritis in various parts of my body and have been thinking about it several times to switch to an electric assist bike. It would take the pain of my knees at some sections of my route I commute to work.
Another reason why they are so popular in Europe: People in the 70s and 80s still use them as utility and leisure vehicle. Honestly I have never seen an 70+ year old here in the US riding his/her bike to get groceries. Hell I hardly see young folks doing that. My mom (73) does it on a daily basis. And the electric assist bike helps her tremendously to get up hills or overpasses.
So as long as bikes are just seen as sport or leisure vehicles I don't think electric assist bikes will become a big seller here in the US.