Why is ITIL so important?

Almost all services most companies provide today are IT-enabled. That means organizations have a tremendous benefit in creating, expanding, and improving their IT service management capability. ITIL is a powerful tool in a way that:

ITIL provides the guidance organizations need to address service management challenges and utilize the potential of modern technology.
ITIL is designed to ensure a flexible, coordinated, and integrated system for the effective governance and management of IT-enabled services.
ITIL is a best practice framework that guides ITSM delivery. 
ITIL is not a theoretic approach. On the contrary, it's practical (written by experts in the industry) and flexible (can be adapted in any company, independent of the size or nature of the business).
ITIL provides an end-to-end approach to IT service management and integrates well with other frameworks, e.g., Lean, DevOps, and Agile.
The article „Why ITIL?“ https://advisera.com/20000academy/knowledgebase/itil/ will provide more details.