We take it for granted today that we can hear any type of music at any time but before the development of recorded music it was a struggle for many even well known composers to get their work heard if it required large orchestras.
Arnold Schoenberg admired Mahler and we have to thank his industry for arranging Leider Eines Fahrenden Gesellen and Das Lied von der Erde for small forces which give singers and players a chance to perform these masterpieces more regularly in a more intimate setting.