Maybe people aren't intentionally stealing credit in the sense that they want people to believe that all that hard work is their own when they know that it isn't, but they are stealing credit by omission.

If you learn a song from somebody else's CD it doesn't hurt to say 'this is who/where I got it from'. That's only one credit, not a long list. As you say, if people want to know more than that they can ask and look stuff up for themselves. But if you don't give any credit at all then I think you are implying that it's your own work even if that's not the intention.