Good question! Here are two answers: First, Cliff Richards is well-known in rock-n-roll in the UK, but not in the US. Even if you live in the UK, it might be tough to hear him. When he was younger, he became a big star in the UK, in some part because he stayed in the UK and unlike so many others, did not leave the UK to seek a larger audience in the US. Therefore, he was not as popular. Second, especially in the US, many radio stations are owned by just 4 or 5 large companies, and not by local personnel that stay in touch with their local audience. Therefore, especially in the US, there are some really great artists who cannot get airplay on the radio. If I were you, I would investigate the 1,000's of internet radio sites. Some are highly selective. In fact, I would not be surprised if one played good UK rock-n-roll, with lots of Cliff Richards. Try one of the many sites that carry radio from the US, the UK and all over the world. You'll be surprised.
I used to program radio stations.