The reason is probably twofold: the pattern is genuinely unusual, and it requires the right specimen with appropriate preservation to be recognized.

The two Sulawesi specimens happen to preserve teeth that clearly show this pattern.

The grooves, as described across multiple reports on the study, are deep and smooth — the smoothness indicating that they were produced by the constant friction of a hard, rounded object (a whole nut, approximately 10-20 mm in diameter) against the enamel surface over a long period.

The groove runs around the tooth at an angle consistent with how a person would naturally hold a nut in the back of the mouth, between the rear molars or just forward of them.

The size of the object that would produce this pattern — 10 to 20 millimeters — is a key diagnostic feature.