Kinda weird to have Mariah as a "guest" on a tour. I think she is trying to connect with older audiences, which is really smart at this point. They still buy albums, and that's much more income than streaming. Also, she won't be able to cater to a younger audience forever, not even sure she would be able to releasing an album next year, for example.
Céline Dion is nowhere on the main single charts, but her new albums still sell millions of copies worldwide.