some friendships just suck big time!!

During COVID I got reconnected with my schoolmate, during that time and until last couple of years we shared a bond as best friends. Then I had to move abroad for my studies but I tried to stay connected. However as the time gone by I felt like he was avoiding me for no particular reason. He rarely shared any major life updates (him moving abroad for a year, wedding), which I eventually got to know from our mutual friend. I still tried to maintain friendship but he was busy most of the time. His brother invited my family 3 days prior to wedding over whatsapp (mind you that his brother and mine also shared a really good bond and we live about few km away). No one from my family attended the wedding as the invitation felt like afterthought and He never addressed that either. Now, after all of this, he has been calling me for the past couple of days, but I am in no mood to talk to him. Why do people act like this?