because Google released Nexus 4 and nexus 10 recently, nexus 7 6 months ago.
CES showcase products that are going to release soon. and Nexus are know for being kept as a secret.
its like asking why didn't Samsung show Galaxy S4? because they don't want to.
It was. Tegra used it to compare their new processor and Samsung used it to gloat about their display and processor while announcing their next components
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