It is true that the use of copyrighted material is fair, such as remixes, mashups, or DJ sets. But many upload these works to YouTube or SoundCloud in seconds, they do not care about copyright infringement. Although this work is derived from the original it's important to promote the author or give them different uses, such as remixes making people dance with songs that can not be enacted, or a set of DJs that mix and unite multiple chains to produce an entirely different sound. The creations are worth publishing and the author deserves his money if people love it!