Why is there no pork on the Indian take-away menu?
In the UK you see lamb and chicken on "Indian" restaurant menus, but not beef or pork. I suspect that in the colonial era when the English wanted meat there were goats (near enough the same as sheep) and chickens because both are kept for food but not meat. So are cattle but they're special. There simply wouldn't have been a supply of pigs or the habit of rearing them - and English breeds brought by the colonists wouldn't do too well in the climate of much of India. Maintaining a supply of pork would have been hard. The English in India also used to exploit and increase religious divisions - at times and in places they relied on Muslims. Rumours of pig (and cow) fat being used as grease on rifle cartridges (which had to be bitten) were a factor in the rebellion of 1857, indicating the depth of feeling about forbidden food. 

While many Indians are vegetarian, there are plenty who aren't, and that means there are plenty of dishes using the meats that are available. 

Many if not most "Indian" restaurants in the UK are run by people of Pakistani or Bangladeshi heritage, who tend to be Muslims. This further explains the absence of pork as it's forbidden for Muslims (including just handling it I believe). 

Goa is an exception in several ways. It was a Portuguese colony not a British one. Iberian pig breeds should tolerate the Indian climate better than British breeds. More importantly, Goa doesn't have a large Muslim population (8%, compare with the UK at 4%). Goa was ruled by the Portuguese before and during the Mughal empire, which had a huge influence on Islam in the rest of India.