Why Google didn't announce a new nexus at google I/O

Were you disappointed with Google that they didn't annonce a new Nexus device at google I/O?  I definitely was.  After thinking about it for a while I have come up with an answer that makes sense.  Google has really taken the console approach with its Nexus tablets and smartphones.  They sell them at cost or even at a loss, then make money later when you use them, or buy games.  So why would they work tirelessly to create a new tablet when their old one is still up to par, and they don't make money selling a new one to you.
 I believe that Google will not release a new Nexus, till their tablets and smartphones are obsolete to the point of affecting sales.  Right now their still selling well and their is no need to create a new one.