Put differently, one might conclude that the unique role of Enterprise in the Federation's formation (perhaps coupled with the previous history of ships of the same name) might have garnered it a permanent place of honor.
This is how I've always viewed the E's status as "the flagship"; sort of going hand in hand with why all Starfleet personnel now wear a variant of what was once the Enterprise
's insignia (an unofficial explanation, of course, but I happen to like it). I just go with the notion that it's going to be that way until another ship and crew distinguishes themselves in a manner that eclipses the voyages of the original Enterprise.
(Not that any such shit is evah gonna happen. Not on my watch!