AES is the main block cipher in use today, standardized by NIST. Camellia is a Japanese standardized cipher. ChaCha is a fast stream cipher specified by Bernstein and incorporated into TLS with support from Google.
Serpent and Twofish were AES last round candidates that didn't make it. Serpent is not that fast, and Twofish is relatively fast but not compared to AES when hardware acceleration is used. Both are block ciphers that are really not needed as long as we deem AES to be secure.
Threefish was mainly designed for the Skein hash function. This tweakable block cipher is not used much. It Skein had been chosen as SHA-3 then it would have stood a better chance. For now an authenticated form of Keccak would make more sense.
So yeah, two standardized ciphers and a fast stream ciphers are supported, none of which are broken. There is no reason to include the also-ran's and a cipher made specifically for a hash function which was also not standardized.