They undoubtedly are interested in Campbell, but he's not so interested in returning.
Well, that was prior to the release of CR. After its immense success, and perhaps a bigger paycheck offer, he might change his mind. He doesn't appear to have anything else on his schedule (though I'm sure he's getting offers after CR).
Here's something interesting. Your comment sent me back to IMDb to check on Campbell's schedule. Last time I checked--three months ago or so--three or four projects were listed as being in development. Now there's nothing shown at all. Could this a sign that he's been clearing his schedule for Bond 22?