Indie is a fairly new¹ genre of music which was added/invented/dreamt up to serve a rather particular purpose and group of individuals. These particular groups of individuals are usually artists, in the loosest sense of the term. That doesn't mean they like to play around with watercolours and big sheets of canvas but that they usually like to play around with guitars and drums and cymbals. In this they are very similar to rock musicians. The difference is that rock musicians are usually good at composing music. In the opinion of some, the manic tuneless droning of indie is too irritating to be classified as rock, so a new genre was invented to persuade people that their sounds were indeed a serious type of music and that people should pay them good money for it, which many of them do.