Up until the 80s and 90s, stations signing off on the FM band, and AM stations with 24 hour licenses was quite common. Usually Midnight-5AM, sometimes every night, sometimes once a week. Same with TV

Usually for maintenance. Sometimes because they had no programming to run overnight. Sometimes because they couldn't afford to have someone on staff 24 hours a day.

With the advance of automation, and the FCC relaxing the rules, it became less common.

As recent as a few years ago, possibly still, WSMI in Litchfield, IL signs off at Midnight. Their AM station is a daytimer and also discontinues programming on both the AM and the translator at night. This is generally not the case with AM stations running translators. They have 1 station in the cluster that remains on 24 hours a day, WAOX which runs Westwood One Hot AC. When WSMI signs off, they say "For continued good listening throughout the night, tune to WAOX 105.3FM" These are very small radio stations in a small rural town. I believe they do it because they have nobody on staff overnight and do not carry satellite programming. They could fix that but have not.

Again, it causes wear and tear on the transmitters shutting them off overnight