Why did Leopold von Schrenck group several Siberian languages under the Paleo-Siberian name?

In the mid-19th century, the Baltic German zoologist and explorer Leopold von Schrenck grouped several Siberian languages under the name "Paleo-Siberian" because he hypothesized that they were the remnants of a formerly widespread language family.1

Schrenck believed these languages had been pushed into smaller, isolated enclaves by the arrival of more culturally vigorous groups, specifically speakers of Uralic and Altaic languages. While modern comparative linguistics has determined that these groups are not genetically related and never formed a single language family, Schrenck’s hypothesis was accurate in noting that languages such as Yeniseian, Luorawetlan, and Yukaghir were spoken over much larger territories in the 17th century than they are today.1