Why do people become hardcore fans?

I dont know if this is the correct reddit but it seems like it so I will write on.

Why do people become fan of something to the point they defend it like their life is depend on it?

I mean I can understand enjoying watching a sport I also watch F1 too. But I would never fight nor spend more money than needed for it. I also love reading stuff about Warhammer 40k but I would never argue its better than Star Wars etc. Same logic can be applied to brands and products as well. If I like something I talk about it but never defend it unless its about healthcare.

For me its pointless these are all products for us to consume we pay for these things.

I just don't get the mindset of beign a hardcore fan of something?