There's this idea that someone shouldn't run against an incumbent. It goes against both parties. The boomer generation was a large group, they often see the world in a more common way (that world of the 50s and early 60s?), they still want to see themselves as being in power, even as they are all getting close to age 80 (made a typo here originally, I put 60 instead of 80). They don't want to give up. That's why these elderly politicians stay in power.