The short answer: Money. Longer answer, well, still money: “The reason for the sudden glut is not only that documentary makers have been inspired by the surprise success of documentaries such as 2012’s Searching For Sugar Man, or Asif Kapadia’s Amy in 2015. What investors have also noticed is the great power of these films to promote a music label’s back catalogue. … ‘A compelling synergy exists between movies and music.'” – The Observer (UK)