We are talking about in-the-city commuting. The local roads/streets at some stage of poverty are full of mopeds and bicycles, with very few cars. When people have no choice. When they have a choice, they could get better bicycles or mopeds. Instead they get more cars, before these cars are even convenient to use (e.g. you may get stuck behind a bicycle with a produce cart for 10 minutes at 5mph as mopeds stream around both of you).

These cities start out in no way optimized for cars, basically by definition (nobody has cars). The reasons cars do better in them too, before the govt responds with more car infrastructure, is because cars are just simply better in terms of convenience. If people wanted to continue cycling after they get more rich, the govt could have built infrastructure for that much cheaper and easier.

Also btw, no matter what, bicycling is still marginal in most climates and for many people who are not fit. The real thing to discuss is transit... many of the middle-income and even poor cities have great transit, but people don't clog the transit and then grudgingly switch to driving, it's the other way around :)