Larray Seltzer points out that Java lost to Flash and AJAX:
Mostly, in the end, it appears that Java on the client lost out to Flash of all things! (…) It couldn’t even be competitive in the most inessential of tasks.
Let this be a lesson to all of us. You can have the nicest framework in the world, you can have the best arguments in the world, but if you are not providing immediate value to your users, you are dead in the water.