As for why:
Okami - main character is a dog. Okay, a wolf. Also too stylized for mainstream tastes.
Zack & Wiki - Niche genre, cartoony style probably didn't help but it works for Sam & Max and Strongbad...
No More Heroes - Art direction made this niche. Overworld like GTA but kinda amatuerish in comparison. But great game.
Marble Mania - Too expensive, too short
Pro Evolution Soccer (PES) 2008 (Release months after the other versions, same for the upcoming 2009)
de Blob - New IP, new genre, too cutesy, can't save mid-level. No co-op.
Boom Blox - Might make 1m when price drops to $20. Getting a sequel.
Medal of Honor : Heroes 2 - Broken people in online multiplayer really hurt (everyone walks around like an old man with a broken waist), meh graphics but good shooter. Best shooter until CoDWaW
Godfather Blackhand edition - Gameplay as kinda flat aside from shooting and beating people up. Really should have sold 1m. Doesn't appeal to kids, women.
Bully Scholorship Edition - As above
Pinball's Greatest Hits The Williams Collection - Niche but amazing. Might hit 1m
Madden NFL 2009 All Play - Too kiddified??
Lego Indiana Jones (will hit a million)
Tiger Wood PGA 09 (Came out right as Wii Motion Plus was announced, which I'm sure will be used in next years version. That didn't help sales)