Monopoly prevention. Once the api is on the blockchain, no one can build a wall around it and charge an entry fee.
The end benefit to the consumer being monopoly prevention isn't likely to outweigh the service guarantees of a centralized service.
What if the broad spectrum of Craigslist service providers included car drivers who could (somehow - hand wave) offer rides on Craigslist?
How much confidence would you have in them?
What condition would you expect their cars to be in?
What kind of driving record could be expected from the drivers?
How would you choose a driver from that spectrum?
Would you expect to pay less or the same as for an Uber ride?
Under what circumstances would you just avoid using a Craigslist driver altogether?