You had to install the JVM. It often broke or bugged you to update. UI usually felt off or janky, and unresponsive. At the time, Java applets were huge compared

You had to install the JVM. It often broke or bugged you to update. UI usually felt off or janky, and unresponsive. At the time, Java applets were huge compared to typical web pages, and had crap performance. By the time hardware and connections improved enough to make the last two things less of a problem, JavaScript could do most of the useful things the JVM could with fewer security risks (and hardware was fast enough that that wasn't also so slow that no-one would tolerate it, as it would have been earlier). [EDIT] Oh, and it had to compete with Flash and Shockwave, which had (barely) fewer issues with plugin breakage, very nice authoring tools (still unmatched, AFAIK?), and, despite having crap performance, still performed better than Java applets. Plus a whole lot more fun things used them so normal people had a motivation to install them.