Looking at my parents and their siblings (varying degrees of almost no contact to some contact with one exception that is good), and looking at my sibling (really good), it has nothing to do with you. It's just, two people that shared an environment growing up, and those two people can be close or not.
I feel very grateful for my sibling, but that's just it. We happen to have the personalities that match.
It's not your fault.
Got an older sibling by 2 years. We don't talk weekly, but we are still quite close when we do talk. Always have been close. Never big fights and usually got along really well.
As kids we used to "manage a business" together (it was plushie based) - we entertained ourselves during long car rides with that business.
I get along really well with their partner, I am like a mix between the two of them. We can talk about everything. They called me when they had shit going on (like their gender), they took care of me when I was suicidal.
We are early thirties