Cardi is likable, and she already had a following before LAHH. She also knew when it was time to leave. Even on the show she centered the storyline mostly around her music.
Although Joseline has some cute songs, it took her way too long. We've watched her be this psycho ass character with minimal talent for too many seasons. And her earlier attempts at music were terrible. Plus, her reputation and image are not exactly inviting. I think Joseline is likable in her own way, but not in the way that would ever be taken seriously in the music industry.
It also helps that Cardi isn't selling sex, and she's hopping on the rap sound that's hot right now. This stripperella mess Joseline is serving ain't going nowhere.