There have been others but they're generally bad, and more significantly, they're by websites that get little traffic. You would need to be in the long game. To want to build up an audience over a long period of time. ESPN is the place for WCBB because it has most of the games (so built in advertising for Creme) and it has the rights to the tourney.
And filling out a full 64 bracket is not that easy. To understand all the bracketing rules, study past brackets, know all the current teams quality, and fill in everything in logically/correctly takes some work.