I'm pretty sure all have the same root reason...it just varies how badly they needed the revival of their careers
Being paid millions to judge talentless nobodies, to stay relevant all while NOT having to put effort into making music/promoting a record/touring and performances. These girls must be having the time of their lives.
I don't know why Xtina and Mariah are doing it, but for Britney, she only does it for her vacation when she is not releasing her new album anytime soon. she's maybe doing it because she is bored but Simon pays her big number and treats her like she's a god, so why would she deny it?
Justin Timberlake - Best Male Artist
Bruno Mars - Most Global Male Artist
Hunter Hayes - King of Country Music