It's very difficult to get a public system to cover every route and part of the city that needs transit, but most city authorities are reluctant to license cheap private jitneys. The public system employees are usually well paid and organized to oppose competition and private taxi companies charge much higher than market rates and are very well positioned to spend some profits defending their oligopolies.
There are eight first world megacities -- cities over ten million population. I wonder if they each have an emerging institution like this.
I understand that in Los Angeles, where the busses are awful and the infrastructure is laser focused on exclusive use of private motorcars, has dollar vans in the Spanish-speaking communities. I'd be interested to learn if the Chinese, Vietnamese, and Korean speakers use those or if they have their own.
In Mexico City, the city has simply licensed dollar vans with just the minimal oversight necessary for public safety. They've all painted themselves green and white and the informal routes have firmed up but there is still -- decades later -- no map, public or private, of the routes of the most common form of transit in this modern city of 22 million. The routes are set and reliable; there's just no central authority to collect information.
Tokyo has built the most extensive rail system in the world by far. I don't know if that has been enough to pre-empt the emergence of informal vans. Seoul has been building fast to catch up building a similarly extensive network.
I wonder about London, Paris, and Osaka.