If the USA kept the status quo of being an ally it would never be a problem. It could only be a problem if the USA was hostile so the Danes could block additional bases (which had never happened, the USA built multiple bases in Greenland during the Cold War).

Leaving only one reason for wanting to rip apart the old agreement: in case the USA wasn't an ally anymore.

I mean, I ain't saying you're wrong. I don't like it, but the idea of non-transactional international relations is probably over...