Cross Keys Inns appears to have been a chain of two motels owned by The Rouse Company, the developers of the planned community of Columbia, Maryland.
Here's a 1970 article, announcing the two motels:
https://www.baltimoresun.com/marylan...603-story.html
At that time, only the Baltimore location was to be called the Cross Keys Inn, the Columbia one was to be called the Columbia Inn. Eventually, they both opened as Cross Keys Inns, and the Columbia property took on its originally intended name in 1982, when they added the tower.
Here's a matchbook on eBay from the 70s, showing them both operating as Cross Keys Inns:
And here's a matchbook on eBay from after the tower wing was added and the name was changed:
You're right, I have no idea why the ancient motel wing hasn't been demolished. It was disingenuous of them to advertise the hotel, when it was a Sheraton, using photos of only the tower wing, when half the rooms are in the old motel wing. And it seems that'll still be the case.