What happened in the years leading up to 2005, or perhaps in 2005 specifically that caused this blackout? Where did all of the Java desktop developers go?
Before 2004, there was a much wider perception that web applications were fundamentally limited by their latency, and if you wanted a really rich, interactive user experience, like Winamp or Outlook, you had to make a desktop application.
Then Gmail launched in 2004 and Google Maps launched in 2005. At that point, if you wanted to make a web-enabled experience with a high-quality user interface, it became more and more clear that you should build the client side in HTML + JavaScript and the server side in whatever you wanted, possibly Java.