Why do most individual Papuan languages have relatively few speakers?

Most individual Papuan languages have relatively few speakers because the region is characterized by a highly complex and fragmented linguistic environment. There are hundreds of distinct Papuan languages, and the average language family consists of only about 25 member languages. Consequently, the number of speakers for most individual languages is generally fewer than 3,000, with many having fewer than 100 speakers and some even fewer than 50.1

This high concentration of numerous, small speech communities within a relatively confined area has historically encouraged widespread multilingualism, as members of a community often learn the languages of their neighbors. Furthermore, this fragmentation has fostered the development of trade jargons and has led to instances where speakers shift their language allegiance toward the tongues of more powerful or economically advantaged groups.1