Making friends as a 31M: why do people gatekeep their social circles? How on earth do I make friends then?

As a relatively new immigrant from a SE Asian country who has had multiple social circles from my home country and has made multiple friends as an adult, I see even people who are SE Asian immigrants gatekeep their social circles. Fine if you just want to meet me because he/she is my point of contact.

It's as if everyone who immigrates to NZ becomes white Kiwi- gatekeeping friends or not wanting to be friends at all. The excuse is that I "don't know all these people". Well if I do not have a chance to get to know them how would I know them?

How come? I did join a local church (and yes I do believe in the religion) but it is not enough and I am keen and hungry to make more friends but it is very very very frustrating to not be able to make friends and have a "gang" in a new city and country.