The singer, who recently entered the industry often do not dare risk buying an album to listen to. Therefore, to further promote your music for free, it makes a singer known widely.
Because the singer has recently joined the band, who usually don't dare to risk buying an album and listen to. So loading music, free of charge, to help promote or help make the singer more broadly recognized.
Because the singer is often not just in industry who dares risk buy an album and listen to music for free, so it is to help promote or make known singer in the circle.