There are applications that need to hash data as fast as possible as long as there's a perception of a reasonable security margin. ZFS uses SHA(2)-256 for data checksumming. Some crypto protocols involve HMAC as well as encryption for transmitted data. If a hash can't keep up with line rate on SAS, FC, or many-GigE links, because you wanted maximum security, those users are going to find another, faster, less examined, hash function.

The criteria for SHA-3 is not "as secure as possible". An application that needs as secure a hash as possible should use a protocol that combines multiple hashes of different families.