Must sound change be linguistically motivated?

A number of well-documented sound changes in Austronesian languages do not appear to be either phonetically or phonologically motivated. Although it is possible that some of these changes involved intermediate steps for which we have no direct documentation, the assumption that this was always the case appears arbitrary, and is in violation of Occam's Razor. These data thus raise the question whether sound change must be phonetically motivated, as assumed by the Neogrammarians, or even linguistically motivated, as assumed by virtually all working historical linguists.