Mark Sutherland It was one of the highlights of the U.K.’s biggest music awards show — but mystery surrounds why the Pet Shop Boys didn’t join Elton John and Years & Years’ performance of their classic song, “It’s a Sin,” at Tuesday night’s Brit Awards.Elton and Years & Years’ Olly Alexander pre-recorded their cover of the song — originally released on Pet Shop Boys’ 1987 album, “Actually,” and a U.K. No.1 and U.S.