That's because Java used the old piece-of-shit NPAPI (Netscape Plugin Application Programming Interface) from 1995, first released in the NetScape 2.0b3 Plug-in SDK:
https://en.wikipedia.org/wiki/NPAPI
Problems Found with the NetScape Plug-in API. By Don Hopkins, Kaleida Labs:
https://donhopkins.com/home/archive/netscape/Netscape-Plugin...
More about Netscape's fleeting obsession with Java and Javagator in the pre-LiveConnect/XPConnect/NPRuntime/ActiveX/DHTML/XPCOM/XUL days:
https://news.ycombinator.com/item?id=22708076
>I hope NetScape can come up with a plug-in interface that is good enough that they can implement their own navigator components with it (like the mail reader, outliner, progressive jpeg viewer, etc). The only way it's going to go anywhere is if they work closely with developers, and use the plug-in interface for non-trivial things themselves. Microsoft already has a VRML plug-in for their navigator, so presumably they have a plug-in interface, and from what I've seen on their web site, it may not be "good enough", but it's probably going to do a lot more that you can do with NetScape right now, since they're exposing a lot of their navigator's functionality through OLE. They seem to understand that there's a much bigger picture, and that the problems aren't trivial. Java isn't going to magically solve all those problems, folks.
Early Browser Extension Wars of 1996:
https://news.ycombinator.com/item?id=19837817
>Wow, a blast from the past! 1996, what a year that was.
>Sun was freaking out about Microsoft, and announced Java Beans as their vaporware "alternative" to ActiveX. JavaScript had just come onto the scene, then Netscape announced they were going to reimplement Navigator in Java, so they dove into the deep end and came up with IFC, which designed by NeXTStep programmers. A bunch of the original Java team left Sun and formed Marima, and developed the Castanet network push distribution system, and the Bongo user interface editor (like HyperCard for Java, calling the Java compiler incrementally to support dynamic script editing).
More about browser extension APIs:
https://news.ycombinator.com/item?id=27405137
>At the time that NSAPI came around, JavaScript wasn't really much of a thing, and DHTML didn't exist, so not many people would have seriously thought of actually writing practical browser extensions in it. JavaScript was first thought of more as a way to wire together plugins, not implement them. You were supposed to use Java for that. To that end, Netscape developed LiveConnect.
>Microsoft eventually came out with "ActiveX Behavior Components" aka "Dynamic HTML (DHTML) Behaviors" aka "HTML Components (HTCs)" that enabled you to implement ActiveX controls with COM interfaces in all their glory and splendor, entirely in Visual Basic Script, JavsScript, or any other language supporting the "IScriptingEngine" plug-in interface, plus some XML. So you could plug in any scripting language engine, then write plug-ins in that language! (Easier said than done, though: it involved tons of OLE/COM plumbing and dynamic data type wrangling. But there were scripting engines for many popular scripting languages, like Python.)
Javagator Down Not Out:
https://www.cnet.com/tech/tech-industry/javagator-down-not-o...
>Though Netscape has ceased development efforts on its Java-based browser, it may pass the baton to independent developers.
Shockwave (the Macromedia Director Player Library) came long before Flash, and it used NPAPI (and ActiveX on IE), but later on, Google developed another better plug-in interface called "Pepper" for Flash.
1995: Netscape releases NPAPI for Netscape Nagivator 2.0, Macromedia releases Shockwave Player on NPAPI for playing Director files
1996: Microsoft releases ActiveX, FutureWave releases FutureSplash Animator and NPAPI player for FutureSplash files, Macromedia acquires FutureSplash Animator and renames it Flash 1.0
2009: Google releases PPAPI (Pepper Plugin API) as part of the Native Client project, suddenly Flash runs much more smoothly