I'm not sure whether you're pointing the blame at the publishers. Retail, ultimately, decides what games are successful by the amount of stock they buy - retailers have probably been hit by HOTD Overkill, The Conduit, Dead Space and have no wish to take a risk on yet another 'core' title.
But even then, retail is taking its prompts from the Wii demographic - if there is not the audience there, things just ain't gonna sell. I am starting to believe, sadly, that the audience is not there.