为什么java applet /javafx没有被广泛使用?(为什么我不应该把它们用在RIA上)

Java is one of the best managed runtime technologies we have. It has very high performance VM which allows to achieve performance close to C. The amount of high quality open source libraries is incomparable to any other platform. However, despite it was the first dynamic client side technology to appear in browsers (Applets), it isn't used widely now. What are disadvantages of Java which make people use JavaScript + HTML5 or Flash/Flex instead of Java for RIA? Why should I use them despite they are not as pleasant for a programmer as Java?Java is one of the best managed runtime technol