It represents a decision, at the community level, that this burial was worth this investment.

Why would a community in such constrained circumstances make this decision?

The most straightforward explanation is the one already suggested: the child had high social status, likely inherited from high-status parents.

In societies organized around lineage and heredity, the social position of an infant or young child is the position of the family into which they were born, not the position they have earned through individual achievement.

If the Mal’ta community had hereditary social hierarchies — if some families were more important than others in ways that persisted across generations — then the child of an important family would be buried with the trappings of that importance regardless of how long they had lived.