Seeing as worb has already been implemented in yoob, why do this? It's not like I can say it's "now playable online", because it already was. (Or if not "playable", then... "play withable"... or whatever.)
Well, the security track record for Java applets has been rather awful lately. Certainly, applets aren't going away, but they're quickly falling out of fashion. Updating your browser may, reasonably, disable Java. We may one day, not far off, see the JVM stop being shipped with browsers, and available only as an add-on.
And that all means I have to tell you to install and/or enable Java in your browser, which defeats the idea of reducing the install burden for esolangs, which was one of the original goals of yoob.
The newer yoob.js framework, which uses HTML5 instead of Java, is still pretty messy and ad-hoc, and lacks a few things that would be nice to have, like adjustable animation speed. But the more things, like this, that get implemented in it, the more it will mature.