I think it takes time for demand to build. Certainly cities like London have seen huge growth in bike use. In my own home town(which is by no means flat) I'm seeing lots of cargo bikes, especially around tge school run.

To your point on bike owners not contributing to the economy. They probably have a similar income, and are paying similar taxes. They are still buying groceries. But where they choose to spend their money is different. It's all still economic activity though.