Expansion of tafoni seems to be based on weathering (seems reasonable enough.) But what creates them in the first place? There are a number of explanations online (Wikipedia lists eight plausible causes!) Many websites trying to give a simplified explanation simply say "salt weathering", but from a brief search it's clear that salt weathering is not always the cause of tafoni . They develop on a wide range of rock types, from granite to sandstone to tuffs and conglomerates, and in many situations where they'd be expected to develop they don't.
From what I can tell, they seem somewhat mysterious, and there are explanations that make sense in some cases but not every case of tafoni is well explained. Is there a widely accepted explanation for the formation of tafoni?
Picture of tafoni (Martin Sharman, Wikipedia):
 for example: page 75, Arid and Semi-Arid Geomorphology, Andrew S. Goudie