Why are body parts and close kinship relations often treated as inalienably possessed in Oceanic languages?

In Oceanic languages, the distinction between inalienable and alienable possession is a fundamental structural feature used to categorize the nature of the relationship between a possessor and a possessed noun.1

Inalienable possession is used for items that are inherently or naturally connected to an individual, such as body parts, specific kinship relations, and personal attributes like one's name or shadow (which is often associated with the soul). Because these elements are considered inseparable from the person, they are marked by suffixing a possessive pronoun directly to the noun, as seen in the Fijian example na mata-na ("his eye").1

Conversely, alienable possession applies to items that are not inherently part of the possessor, such as houses or food. These relationships are expressed using a preposed classifying particle that specifies the nature of the connection—such as whether an item is intended for eating or drinking—rather than suffixing the pronoun directly to the noun. This system reflects a linguistic categorization based on the degree of control or permanence inherent in the relationship.1