In this, it probably learned its lesson from inventor Dean Kamen. In 2001, Kamen unwittingly unleashed a tidal wave of media hype prior to his unveiling of what became the Segway, an elegant, simple, two-wheeled personal transport. The buildup was huge and the letdown made the actual device appear somewhat foolish and left sales on the launch pad for months afterward.
Let's take this apart and look at some of the possible reasons for Google not making an announcement:
Perhaps Kurzweil's hiring is largely a brand acquisition. The inventor's specialties in "machine learning and language processing" are important technological concerns the company has. It's original search engine was an improved algorithm enabling people to more easily find what they were looking for. Every Google product, including Maps and the self-driving car, are stamped with this ease of human-machine interaction.
My favorite example of this is the Google Doodles. They can be incredibly complex, but the presentation is so clear that we learn how to use them simply by playing with them. They're the perfect Google brand icon: a little machine that acts like it knows us.
In this scenario, Kurzweil is supportive, but more of an honorary engineer, an inspiration to the researchers, someone who might toss out an idea or two to fire them up but is largely out of the picture when it gets down to marketable projects.
Kurzweil's name is one of those that is widely known in certain circles -- and those circles can be pretty disparate -- but is still not a household word by any stretch. It could well be that Google just doesn't see this hire as being of interest to investors or to the public.
I can't discount this possibility completely, but on its own I find it hard to believe. New hires are usually touted to the media as the best possible move for any company. Even if we had never heard of Ray Kurzweil, Google should be singing the praises of its new Director of Engineering from the rooftops.