What does Salmons being a free agent have to do with anything? If you trade for Salmons you get a young player with potential and a player with an expiring contract (and I'm not sure he is a free agent this summer). Teams actually like to see players with expiring contracts because that gives potential cap space. Korvers contract isn't that big either, he got a long deal but its not that much.
I think the thing that turns other teams off about Johnny is that he hasn't proven anything yet in the NBA. Sure, he's been tearing up the summer leagues, but he has shown little to be excited about (in terms of consistency) for other teams to be seriously interested in him. Sure, he'd be involved as a filler in some deal, but he certainly won't bring much back if he was traded by himself.