Through the years many siblings drift apart or decide to get angry about something and vow to never speak to them again. Under certain circumstances that is necessary.
However, in the vast majority it over stuff that when you look back at it was really so trivial in nature. Then the years pass and you reflect on why you have no contact with your siblings at all? The sad reality is that nobody wins in the long run.
I know with mine I really have no idea why we don’t? They for whatever reason decided that I did qualify to be their brother. To this day I carry any ill will towards my brother and hope and pray that they are have long and fulfilling lives. In the end we all lost and that is a loss none of us will ever realize the cost we paid!