The Army turns green with jealousy over the existence of the Marine Corps, particularly their elan, panache, esprit de corps, and sang froid (French for cheeky upstart). The Marine Corps stole a march on the Army with the Banana Republic Two Step (Expeditionary Warfare) which folks forget is their traditional role going back to their 1776 raid in the Bahamas to disrupt British operations.
As long as there are American interests that span the Seven Seas, both the Navy and the Marine Corps are front and center in the ranks of the long serving professional force, particularly in those years in between Big Wars which tend to be Bananas and Nuts.
The Army and Air Force understand at a visceral level that the absence of a serious clear and present danger, there is no pressing need for a long standing professional Army or Air Force. What reinforcements needed by the Navy/USMC can be provided by Reserve and/or Guard forces. The fact that no serious big war threat faces the US is impressively documented by the return of Air Force and Army units to Festung Kansas where their forces are closer to the Middle East than either Europe or Asia (Globe please).
What is also damning is the Pentagon effort to Navalize the Army by creating Brigade Combat Teams be deployed like LGBs (Large Gray Boats). Rotating brigades is a copy cat of rotation of ships, except that some ships swap crews and go back to sea.