Is it mandatory to enforce NFPA 13 for insurance?

NFPA 13 only applies to specific types of occupancies and the requirements for enforcement would depend upon the "authority having jurisdiction", local ordinances, and state fire codes. Compliance with such codes is frequently a pre-requisite for obtaining insurance.

On the other hand, other facilities may have different requirements (e.g., NFPA 13D or NFPA 13R), or the code may modify the NFPA 13 or NFPA 25 requirements (e.g., NFPA 101 chapter 33 modifications for NFPA 13R in "existing residential board and care facilities"). Your local fire marshal and insurance company will help you with specific requirements.