Plenty of Anglo-Indians marry outside the community and are perfectly happy. But there are things that are difficult to explain to someone who did not grow up with them, and they tend to appear years in, not at the beginning.
The things that need no explaining inside the community
Being asked where you are really from. Repeatedly, all your life, by people who mean no harm. Someone from outside will not understand why the hundredth time lands differently from the first.
English as the language of the house. Not as an achievement or an affectation — as the mother tongue, the language of grandparents and of thinking. It is routinely read as pretension by people who do not know the history.
Christmas as the fixed point of the year. The baking starting in November, the particular sweets, the house full for a week. Not the festival everyone else has around it.
Being a minority inside a minority. Not quite the Christian community around you, not the surrounding majority either.
Everyone knowing everyone. Four names and two schools and a connection surfaces. To someone from a large community this seems like a coincidence. It is just how it works.
Family abroad. Nearly every family has some. The empty chairs at Christmas, the calls at odd hours, the cousins you have met twice.
What this means practically
Not that you should marry within the community. Many do not, and it works.
It means that if you marry outside, some things will need explaining more than once, and a few will never quite land. That is survivable when both people know it in advance. It is corrosive when one of them thinks the other is making a fuss about nothing.
And what marrying within it gives you
The shortcut. Someone who already knows what the food is called, why Christmas runs the way it does, what the question about where you are from feels like. Nothing needs translating.
That is a real thing, and it is the reason many families would rather search harder and further than search nearby and outside.
Neither choice is the right one in general. But both work far better when the conversation has actually been had.