It’s the metal umlaut invading other genres of music.
Briefly, in the seventies, metal bands started adding diereses (and other diacritical marks) to their names or song titles to look mean, German, soft, cool or whatever (the reasons are not always known and vary from band to band). This phenomenon was named metal umlaut. While it was never limited to metal, it now appears to have invaded pop.
Note that two dots (dieresis) can also be used in English to indicate that two vowels following each other are not a diphthong (e.g., in reüse), but this is rarely done nowadays.