Why Camellia has 4 Sbox I asked a question about using 16 different Sboxes in AES each for one state byte instead of using same One Sbox for substituting 16 state bytes (See the Question Increase in AES SBox). The answers i got are like given below


  at least one disadvantage of using 16 S-box to change the 16 bytes. The size of the code and the look up tables (should you use such implementation) would increase the size of the code. This increases the surface of exposure for cache timing attacks.


Now i wonder, why Cameillia designers used 4 Sboxes with almost similar properties? What is the main advantage of using more than one? Even Twofish uses 4 key dependent Sboxes.
The only way you will have a certain answer will be by mailing their designers.

Using multiple S-boxes increases the size of the code and decreases the possibility of working with different blocs in parallel.

Using a single S-box also simplify the way the specifications have to be written. The simpler the specifications are, the less prone to make error at the implementation step you are.

Not related to Camellia but on the same idea:


  JP Aumasson: why nobody uses SHA-3? FIPS 202, a 29-page specs written for cryptographers, not for users [source]
  
  JP Aumasson: seriously NIST, in 2.5 years no one had the idea that, perhaps, it would be good to simplify that thing? like, ditch the greek part [source]


However, using a single S-box implies some sort of symmetry in your bloc cipher which MIGHT be the reason why the designers of Camellia preferred to use 4 S-boxes instead of only one.