Satoshi didn't want a significant amount of publicity as Bitcoin was still in the early stages and it needed healthy, slow growth.
Actually, some of his last posts were on that topic, and IMHO it could have been one reason for him leaving:
It would have been nice to get this attention in any other context. WikiLeaks has kicked the hornet's nest, and the swarm is headed towards us.
And at this level, Bitcoin basically can't be advertised as it isn't a company. Individual companies related to Bitcoin advertise Bitcoin as a whole to match their own agenda, but since Bitcoin is decentralised the idea of advertising Bitcoin as a whole would be too costly to whichever group who did it.
When someone creates a great new technology, people find it. Sometimes too fast.