Why is Sardinian considered especially close to Vulgar Latin?

Sardinian is considered the Romance language most similar to Vulgar Latin due to its preservation of an array of archaic linguistic features.1

This closeness is largely attributed to the island's history of isolation. Specifically, the Logudorese dialect, spoken in the central mountains, reflects a period of isolation dating back to at least the 1st century BCE, caused by the repeated upheavals of the tribes living in that region. As a result, Logudorese remains the most conservative of the Sardinian dialects.1

While other Romance languages evolved significantly from their Latin roots, the geographic and historical circumstances of Sardinia allowed the language to retain a structure that more closely mirrors the Latin introduced to the island following the First Punic War in 238 BCE.1