Why Most Blockchain Applications Are Dumb

> For example, someone proposed an Uber-like site that’s operated on a blockchain rather than having one company control the platform. But I want a minimum standard that I can expect from a taxi, and I want a central party to enforce it.

Why does it have to be a central party? Why not have multiple parties competing for how well they vet the quality of taxis and drivers, as well as reviews from the people who actually use the service?