Not because of social media or a formal algorithim but a less formalized one referred to as "socialization" and decided by prior actions of those who came before, some long dead and some still alive today. It was madd up in part of thoughts of thinking people in different contexts and in part unthinking set in stone doctrines. Just like an algorithim essentially with the tweaks by programmers ans input sources providing the "thinking" and the content and program providing the "unthinking".