Why are Paleo-Siberian languages not considered a single language family?

Paleo-Siberian languages are not considered a single language family because they are genetically unrelated. The term "Paleo-Siberian" is a geographical and historical classification rather than a linguistic one; it refers to a collection of languages that are remnants of populations that occupied Siberia prior to the expansion of other groups, such as those speaking Uralic or Altaic languages.123

These languages are categorized into four distinct, unrelated groups: Yeniseian, Luorawetlan, Yukaghir, and Nivkh. Using the methods of comparative linguistics, researchers have determined that these groups do not share a common ancestral origin. Instead, they likely represent a fragment of a much greater diversity of language families that existed in prehistoric Siberia before many were absorbed by more culturally or numerically dominant neighbors.12