I think it was because 1) many AM stations were looking for FM counterparts/translators, etc. The 101.7 was a good fit and 2) the signal isn't that great in Wilmington. (If you do a quick look on Radio-Locator, when you pull up "Wilmington DE," 101.7 isn't even on the list!) I can't image a station with that signal, with no decent sized city in the primary coverage area, could make much money -- especially as an urban.
101.7's stick is in western Cumberland County. No wonder Delmarva flipped it.
ixnay