interesting question - there was discussion in early “Q” days that the Marines are under special jurisdiction by POTUS - they provide security and transportation.
I’m guessing 2 reasons:
1) Marines provide security outside their bases for embassies (which are US soil), White House and other such places.
2) They do not want to hinder the Navy inside territorial waters from prosecuting intrusions. Internal Rivers fall under the Army Corps of Engineers “jurisdiction” as I’ve always understood.