hornet61 said:"and there's no shortage of them to play."
for the 4,000,000,000,000 time.
There's a famous quote attributed to James Taylor, but I'm sure he wasn't the first person to say it. He was asked how he was able to sing the same songs over and over again in his shows for over 40 years. He said "They may be the same songs, but the people sitting in the audience change, and it's their faces and reactions that make the songs different."
With radio, the audience changes too. They go through different stages of life. New people come into a format that might not be familiar with the war horses. To others, those songs are the fabric of their lives. People tune in to the radio station at all times of the day, and may only stay for a short time, so you need to hit them with your best shot. If you go to a James Taylor concert, and he doesn't do "How Sweet It Is" or "Fire & Rain," people will be disappointed, regardless of how often he's performed it. He may work in something obscure or something new, but that's often when people head to the bathroom or for a beer. You can't do that on the radio.
I may have added this before your comment, but there are ways to freshen up a classic format, and it comes with how you manage those songs. How you group them, rotate them, and present them are all part of the process. No problem doing a specialty show where you throw in something they won't expect, but it should go to a daypart where it won't hurt you. Then promote it so they know where to find it.