ARX functions are difficult to cryptanalyze, thus the reason why it takes longer to reach the optimal cryptanalytical method against it. In the NIST report on SHA-3, it was commented that there is less cryptanalysis against non-ARX functions than say Threefish.

It also shows that the cryptographic community is susceptible to publication bias.

The greatest issue that Keccak (pronounced ketchup) has is that it has a lot of side channels... like Rijndael.