As much as I see your point, being hot isnt Madonnas job. Her job has always been music. Being hot and provocative was just a supplementary factor. It's not like her career was based around being a model and even if it was, that's not a job you can have forever. Same way you can't be an athlete forever, eventually your body doesn't have it anymore and that's natural and completely ok. Most artists that continue to have lucrative careers aren't managing that based purely around sex appeal. It's their music and often nostalgia that keeps them going.

Also, I feel like your Dolly Parton point ignores how much people like her based on culture, her personality, her charitability etc etc more than just because "they are still hot". I mean a huge amount of Madonna fanbase come from the gay male community. I don't them finding her sexually attractive would be the factor that helped hold onto their support.