Sonic Generations probably would have been on Vita if the handheld was released earlier, but Sega did get a really good version of Virtua Tennis 4 out for Vita launch.
As for the rest of the games, the Sonic deal with Nintendo is why Sonic Lost World didn't end up on Vita (or any other formats), though the Vita was also spared Sonic Boom and its two handheld games.
Sonic Team went and made Sonic Runners for mobile, but that didn't get adapted to anything, to my knowledge.