You probably misremember. Java was indeed installed on effectively all browser-capable machines from 1997-200x. All you needed was an <applet> tag, not an <object> or <embed> like other plugins like Flash. Speaking of Flash, it came preloaded for a time, but mostly rode the ActiveX wave for installs. You could not count on it being installed though. I vividly remember the fallback markup when it was unavailable.

Internet Explorer had 90% marketshare in the years around 2004. Netscape was dead. Mozilla/Phoenix/Firefox was a hopeful, not a contender. VBScript was everywhere IE was, and folks still preferred JS, even if their sites proudly proclaimed "Best viewed with Internet Explorer". In the late 1990s/early 2000s, MSDN was full of examples pushing VBScript. It became second nature to myself and coworkers to just reason out what the equivalent JS looked like on the fly. Microsoft absolutely tried its best to replace JS, but devs wouldn't have it, and the number of JS-powered sites was just too large for Microsoft to simply drop compatibility.

It was around that time that Microsoft stopped making updates of any kind to Internet Explorer for years. Folks today really don't comprehend the debt we hold to Mozilla for breaking out of the notion that the web was feature complete.