Would this explain the changes, ie the essential electrical system is no longer required to me article 700?
Yes, NFPA 99 has purview and that technical committee directs the requirements. The NEC technical committee has no choice.
As I recall the only part of the essential electrical system that has to comply with all of Article 700 is the life safety branch.
One of the other big differences is the coordination required in Article 517, vs the selective coordination in Articles 700 and 701. Selective coordination is down to time zero, and coordination in Article 517 is only down to 0.1 seconds.
That makes a huge cost difference in the installation and is one of the reasons NFPA 99 uses coordination and not selective coordination.