There's a difference between taking inspiration from a work of art and actually using part of that work of art in a new work of art. For most of history, it hasn't really been possible to have an exact copy of a work of art that could be used in another work of art; if, in the seventeenth century, a painter saw someone else's painting that had this really neat new way of painting a table or something in it that they really liked, the painter would have to go back home or wherever, and then try to imitate this new style from memory. Now, in the twenty-first century, it'd just be possible for the painter to actually take an identical copy of the painted table and incorporate the exact copy into their art. Same with music; this situation can happen with photos, or audio recordings, or a scan of something, etc. As the technology allowing such reproduction becomes more commonplace, it shows just how ill-equipped copyright law is for dealing with this sort of thing. (Previous to these technologies, the only form of art that could be exactly reproduced would be writing.)