SHA-3 (Keccak) is not a better choice, because it has a considerable performance difference between hardware and software implementations, while BLAKE is very fast in software (or current general-purpose CPUs), which is good for most defenders (as they use  general purpose hardware) and bad for attackers (as the cost of specialized hardware is increased). None of the Password Hashing Competition submissions used Keccak, and even the authors of Keccak recommended against using it for password hashing.