My guess is that it's not purely elevation/weather based, but that certainly is a factor for people's comfort. E-bikes can help with the elevation issue at the cost of being more expensive of course.

What's the level of bike infrastructure available? It can be surprising how protected people need to feel from cars to use bikes over other modes of transit. I personally only bike in bike lanes and will avoid sharrows and walk my bike on the sidewalk if there isn't a lane available. My partner will only bike on grade separated paths. This leads to us mostly walking or taking public transit since we're in an urban area, but both of us would gladly bike if we had a good network of bike lanes to do so.