It's not a tribal thing Venator - it's called culture. A child adopts the religious practises of it's birth country in exactly the same way as it adopts that country's language and food. Children born in France think nothing of eating snails, horse meat and frogs legs, yet those things revile the British. The same goes for foods in Asia such as swallowing live squid in Korea, eating roast cockroaches and eating raw fish in Japan. Yet they find our eating cheese to be revolting (they call it rotten milk). The main religion of a country is instilled in it's people in the same way.
We think nothing in the UK of having time off work for Christmas. The schools close, the shops put up their trees and decorations (in October), millions of people gather together, TV programming changes etc etc. Even people who are not religious expect to have Christmas off. Muslims have Ramadan, Jews have Yom Kippur.
The three main monotheist religions worship the same God whose simply known by a different name (Jehovah, Allah or Yahweh).The only differences in the religions are the methods of worship. Other religions worship different gods or spirits such as in Shinto or African religions. It's a shame the world's religions are so aggressive towards each other and don't readily accept each other side-by-side instead.
It's all called culture.