You never know why they couldn't get anything booked for the night of. That unit might be on maneuvers of some kind, or on duty of some kind.
Jamis -
When, besides when the First Sergeant/Sergeant Major had your butthole in his sights, did any unit not already deployed or on specific stand-by ever, ever, ever schedule anything to conflict with the Marine Corps Birthday?
And what makes you think they wait till now to see about booking a room? That's usually done three or more years out, with a place or two on stand-by in case of fire, flood or zombie apocalypse outbreak. At least that was how "my" Old Corps did things. Lord knows what you youngsters have done to the place since they threw me out in 1971.
stay safe.