Why couldn't they be the Vita's good games? This sucks. Think about what the Vita is right now: a viable platform in Japan and a completely niche system in the West. But its 3 biggest sellers are Western games, the few that actually resonated with the Vita's potential market in the West.
I'm not sure what this means for the Vita. I think it means that the system could have done well in America if Sony had supplied it with high-quality titles that appealed to the Assassin's Creed & COD crowd. But Killzone was an attempt at that -- maybe it was too little, too late. It was certainly overshadowed by the PS4 launch.
What an unfortunately mishandled platform.