House of the dead: overkill is another really good recent release. I'd guess poor marketing and consumer targetting, of those 5 three of them were mature games on the Wii which is a well documented bottomless pit for 3rd parties. VC was amongst the best games of the generation and I hadn't even heard of it until it was already released, they just didn't drum up the hype it deserved.
Bayonetta seemed better marketed and suited for its audience, I'd guess that one sold ok.
Not sure if Sega all stars racings falls under the Sonic umbrella and is safe or not. The naming of it suggests they didn't feel it could carry itself without the Sonic brand.
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Smurf, the cream of Sonic fanboyism