My only anecdote regarding Indians and pork comes from a girlfriend I had a long time ago who was southern indian (tamil and telegu) family. There was no religious directive banning pork but they still did not eat it. Where she came from, pigs were seen as the garbage cleaners of the cities, regularly eating filth, garbage and even corpses. For the preservation of their own health, these people avoided pork which was seen as unclean. She did say that the lower castes ate pork and to avoid associating themselves with a lower caste, they also abstained from pork. In their eyes, the best meat was goat.
Here we see two explanations that have been put forward for this taboo existing in the modern day. In all probability there was no one cause but a mixture of different factors like classism, disease, lack of resources, someone in power not liking ham, etc.