Christian broadcasters will buy a lot of them. They're not in the business of ad revenue. They are ministry.

Couple examples are in West Michigan. A University had a pair of AM signals running an Oldies format there. They shut them down, sold the land, dropped the towers. Michigan's variation of K-LOVE (Smile FM) bought the signals. They didn't have translators but they got some for them. This was a couple years ago. They're still on wire antennas while they try to find transmitter sites. But they bought basically nothing but the licenses and some transmission equipment.

Cumulus looks for buyers first. Usually they don't find them for AMs or even FMs so they turn in the license. Sometimes they do. Townsquare just turns them off and turns in the license. Sometimes it's less time consuming (And therefore costs less money) to try to find a buyer for a station. They probably prefer to avoid the hassle.