Are you asking why nobody has made a website that competes directly with Craiglist, but with a better interface? Padmapper allows you to post listing directly, but it's very difficult to get buyers or sellers to bother with a different marketplace when all the other buyers and sellers are already using Craigslist. You can't beat Craigslist on price, and many non-technical people are already comfortable with the existing system. Convincing them to switch to a different marketplace with fewer potential customers and a new interface is very difficult, no matter how great your features are.
Are you asking why nobody has made a website that competes directly with Craiglist, but with a better interface? Padmapper allows you to post listing directly, but it's very difficult to get buyers or sellers to bother with a different marketplace when all the other buyers and sellers are already using Craigslist. You can't beat Craigslist on price, and many non-technical people are already comfortable with the existing system. Convincing them to switch to a different marketplace with fewer potential customers and a new interface is very difficult, no matter how great your features are.