Why is it human nature for people to want to tell others about their religion?
To pick up the restaurant analogy made by
@sun rise, you want that the restaurant thrives so you can return and have good meals, preferably with your tribe. Keeping it a secret could lead to the restaurant having to close.
That's why your ancestors told their tribe of the field with the good berries. It kept all the tribe fed and the berry seeds were dispersed.
Back to modern times, convincing others to buy a product may lead to that product being produced in greater numbers and get cheaper. That isn't always true. rare things get more expensive when they are wanted by more people but overall the heuristic works and we keep doing it instinctively.
I have no intention to proselytise or try and spread my religious beliefs by converting others to them yet I feel a desire to discuss them with others which is something I try to stop myself doing
People discuss religion for two diametrically different reasons (which often leads to them speaking past each other): you may want to proselytise (spread your religion, get more powerful, get more tithing) or you want to validate or falsify your ideas.
I like to bounce off my ideas off people who are willing to take a look at them and want to know their perspective, information I hadn't integrated yet, told when I made a logical error.
And, following the Golden Rule, when people tell me about their ideas, I assume they want me to critically analyse their ideas and give useful feedback.
I'm sometimes sensitive enough to apply the Platinum Rule. Sometimes people just want confirmation not criticism. And while I can't give that in good conscience, I can refrain from criticising.