I suppose this is the revelation. Since this is your rare genuine post bereft of the fantasy or mystical elements, it would be wrong on my part to add those elements here. However, let me put up some possibilities-
You never felt the connection with them. Maybe thats not the case vice-versa and they genuinely do not wanna spoil your mood so they don’t talk to you unless you feel like talking to ‘em. The younger siblings often complain of the divided love from the parents, maybe this is your mind doing tricks on you.
Your family might have been expecting the birth of a boy. Unfavourable results might be playing its part here in them unable to accept the truth.
Maybe you had a twin and at birth, you as foetus would have claimed the right to your twin’s part of food resulting in part-miscarriage and the family might be unintentionally blaming you for their death.
You might be adopted. Krug might be your blood family’s title but maybe they couldn’t escape the one ultimate truth of life. But your current family adopted you and took care of you. You might not feel the connect, but you should feel the reverence for them if this is indeed the case.
And as Alte pointed out, your mum must indeed be talking about adulthood,
afterall it could be understood only after the age has been reached.
So try connecting with them instead of strangers, your life might change for better.