Covers aren't all that horrible. If someone enjoys playing music and likes to perform, but isn't very good at writing music, then why not perform songs by other people? Or, in cases where popular bands are performing them, it's almost a tribute really, saying "I think this band is awesome" sort of thing. Who knows, maybe some of those people who heard Fred Durst perform Wish You Were Here seeked out the original version, bought the Wish You Were Here album and became a Pink Floyd fan.