It's reminiscent of people adding "no copyright intended" (sic) when posting other people's music online. It seems like intuitions about copyright have been shifting, even if the law hasn't.
I think people actually know it's wrong and legally questionable.
I believe they do it because they simply want to do it and in the back of their minds, hope adding some bogus disclaimer will let them get away with it... because other people seem to be getting away with it.