Why is the term Melanesian limited when describing Papuan and Austronesian peoples?

The term "Melanesian" is considered limited and often misleading when used to classify both Papuan and Austronesian peoples because it obscures significant ethnological, linguistic, and archaeological distinctions between these groups.1

Grouping these populations together as "Melanesians"—in contrast to Micronesians and Polynesians—fails to account for the following:

• Linguistic Differences: Papuan languages do not form a single, genetically unified family; they consist of several dozen distinct language families. In contrast, Austronesian speakers in regions like northern Vanuatu and the southeastern Solomons speak languages that are closely related to those found in Polynesia and eastern Micronesia.21
• Cultural and Religious Ties: Austronesian-speaking communities often share deeper cultural and religious affinities with other Austronesian groups across the Pacific than they do with the Papuan peoples of the New Guinea interior. For example, their religious systems frequently incorporate shared concepts such as mana (potency) and tapu (sacred), which are also central to Polynesian traditions.1
• Historical Origins: The two groups represent distinct historical populations. Papuans are descendants of ancient populations that occupied the Sahul continent at least 40,000 years ago, while Austronesian peoples arrived in the region by sea from Southeast Asia approximately 4,000 years ago.1