Why doesn't a song show up in its own song radio? The song disappeared from its own radio.

[Triscuit714]

Plan: Free

Country: USA

Device: Mac Mini 2012

Operating System: macOS Mojave, 10.14.6

My Question or Issue

A few months ago, I started listening to the song radio for Don Henley's "The Boys of Summer", and at that time the song was listed in the radio. A few weeks ago, however, I realized that the song was no longer listed in the radio, though I could still find the individual song. The same thing happened with Steve Winwood's "Higher Love": the song was listed, then it wasn't. Is this a common occurrence? Is having the song in the song radio now a premium feature?