"Loss of primary station's signal. The translator must be set up to go off the air if the main station's signal is lost." [1] and cites regulations [2][3]
[1] https://www.fcc.gov/media/radio/fm-translators-and-boosters
[2] https://www.ecfr.gov/current/title-47/chapter-I/subchapter-C...
[3] https://www.ecfr.gov/current/title-47/chapter-I/subchapter-C...
There are issues with FCC public licensing to be certain, but the way a lot of stations deal with translators isn't quite above the board considering many stations attempt to follow the regulations (IMO).
I must be missing something, because this seems an arbitrary rule that has no purpose except to increase the FCC’s licensing revenues by allowing them to charge more for “real” spectrum allocation that for a “translator” allocation.