 The picture of nature as a CA is supported by an epistemological desideratum, i.e., having exact computational models of the physical world (see for instance the discussion of ontic pancomputationalism in the entry on  computation in physical systems).  While this is certainly one of the arguments involved, it is not the only one and probably not the strongest. As Piccinini points out, even someone who shares that desire “may well question why we should expect nature to fulfill it” (Piccinini 2010: Section 3.4). 