I grew up in a Catholic family and vegetarian dishes are actively shunned, the absolute only socially acceptable lent option for dinner is fish.
Catholic rules say it's the only meat that one can consume on Fridays during lent. Why? Cause that's the rules. Religious rules are usually fairly arbitrary.
No, this is a weird and popular misconception.
~ 97% of the people in Tamil Nadu and Kerala are non-vegetarian. South India has amazing non vegetarian food.
Meanwhile people in India eat chickens, fish, goats (seemly a popular dish is goat neck? saw some indian chef on youtube making that) and so on.
Also there are suspicions that cows were made sacred in first place to force people to not eat their source of milk, because seemly eating the cows was more popular than milking them, but they are far more useful in certain places for milk than for meat.