Why do shared grammatical traits not necessarily prove that two Siberian languages are related?

Shared grammatical traits do not necessarily prove that two Siberian languages are related because such similarities are often the result of the diffusion of linguistic traits over large geographic areas rather than evidence of genetic affinity.1

In linguistics, it is essential to distinguish between genetic classification, which groups languages by their diachronic descent from a common ancestor, and typological classification, which groups them by structural characteristics. While genetically related languages may share typological features, structural or grammatical similarities can also arise through long-term interaction between contiguous languages, creating "linguistic areas".234

For the Paleo-Siberian groups, which are considered genetically unrelated, observed resemblances in grammatical or phonological traits between them and their neighbors (such as between Chukchi and Yupik or Nivkh and Japanese) are not indexes of a shared origin. Instead, these features reflect the complex history of contact and the spread of linguistic characteristics across Siberia. Consequently, typological similarity alone is not proof of a genetic relationship, as the two systems of classification are based on different data and serve different purposes.123