A lack of infrastructure driving a lack of demand. I love my cargo ebike but it's too bulky to ride on winding sidewalks. I try to avoid roads and unprotected bike lanes wherever possible. My local bike trail network is essential to feel safe when the speed limit for cars is 50kph+ and my bike maxes out at 32kph. Most US cities don't have trails like that where you can easily get anywhere you need to. While I have the battery capacity to get to the next town over, there's no bike lane and the roads are 100kph.
It's also important to note that something like 97% of US bike components come from China. The bike industry was struggling before with low demand post-COVID, but the tariffs are going to be devastating for their entire supply chain.