It was not a superior medium
Its was:
a convenient one
a bit more robust than cassettes and LP's
But the bottom line is the industry realized they could in effect get people to re buy their entire collection and make $$$$ by marketing the above too.
however blinded by greed and ever so shortsighted (aka the GUI, Alto and ZEROX's belief that the copier was the end all be all) the created a perfect medium for sharing individual songs hence the rise of napster etc