...Why Nissan hasn't put the 1.6L I4 turbo that they have in the Juke in to a sentra and slapped some SE-R badges on it?

Can someone help me understand...

This thing is available with a 198hp engine and (according to reviewers) a quite close-ratio 6-speed box. So why isn't that engine in the Sentra? I mean, they've already got the (IMO aesthetically pleasing) Nismo Sentra concept!

Can someone help me understand...