Does Anyone Know?

I have known my birthmother my whole life, but only met my birthfather twice. It was an open adoption. It hurts me that my birthfather isn't interested, especially now that he is getting older. I am waiting to adopt now, and have been waiting almost 5 years. I can't imagine my future birthmother or birthfather not wanting to at least meet their child. Does anyone know why they might not want to? As I wait to find birthparents sOOOooo many questions go through my head.... Thanks in advance.