When java was young, people were excited about writing applets. They were cool and popular, for a little while. Now, I never see them anymore. Instead we have flash, javascript, and a plethora of other web app-building technologies.
Why don't sites use java applets anymore?
I'm also curious: historically, why do you think this occurred? What could have been done differently to keep Java applets alive?
I assume it's because java is a "real", ie. general purpose language. To make an applet, you have to write code, and there aren't any shortcuts.
Now that flash etc have come along, you can pretty much just drap and drop your way through making a cool animation for your website. This is a much lower barrier for entry - you don't have to know how to program in order to get a flash animation working. So flash proliferates, and java applets are hardly used anymore.
The JVM is very widespread, especially in the coorporate world, at least where I've worked, there was always a JVM installed.
I'm currently working on a Java Applet, but in general, I would never an applet unless I had to. But then again, I wouldn't use Flash or Silverlight, either. Applets have a slow load time, and look out of place in webpages. Also, Macromedia/Adobe have outmarketed the good ol' applets.