Is it really hard to imagine this: you're at the water cooler, and one of your colleagues asks you what you're up to. You admit it: you're implementing Java Applets. So the other guy just stares at you for a second and starts laughing, guessing it was a joke!
What I'm trying to illustrate here, is that Sun should have waited until they had the "consumer JRE", and should have launched a new Applet initiative at the same time that new JRE launched. Call it AppletFX, drop the name, whatever... just get that bad taste out of people's mouths. Which brings me to my second point.
2. They announced it too early
Sun probably felt the Adobe and Microsoft pressure in the same market, so the announced their thing ASAP. Guess what, they had nothing impressive to show. Sure, there's JavaFX Script. Sure you can draw circles and make buttons spin. Hell no, you can't use your mouse wheel in JavaFXPad (what gives?). I mean, where's the candy? The impressive story? The leading vision? The cool feature? The great performance? As they say, you only have one chance to make a good first impression.
3. They forgot to include rich video an sound support.
People come for the bling, but stay for the platform. If you haven't got the bling, nobody is there to stay. I didn't hear them announcing anything on the subject. Did I miss that part?
4. Scripting is harder to read compared to XML (for designers?)
Say what you want about XML formats, but people got used to reading XML. Not a lot of syntax to look at, and easily toolable.
Sun is looking at yet another missed opportunity to revive in-browser Java apps. But they do have a nice alternative for creating desktop UI's now.