Why is the Palauan language difficult to describe using regular grammar rules?

The Palauan language is considered complex because it contains numerous irregularities that make the formulation of consistent grammatical and lexical rules difficult.1

While Palauan is classified as a Western Austronesian language, it shares a characteristic common to many languages in this family: a very rich morphology. This morphology functions through complex verb-forming and noun-forming processes, often utilizing affixation to encode syntactic relationships that other languages might express through free words. These intricate structural features, combined with the language's inherent irregularities, contribute to the challenges linguists face when attempting to describe it using standard grammatical frameworks.21