Because lots of things are written in it, it has good library/tool support, is pretty performant, lots of developers know it, and it's good/flexible enough for most tasks.
The inertia of Java projects is huge. IMHO the future of Java depends on the perception that can be created for Java as an attractive ecosystem for greenfield projects.
The reason is pretty simple - enterprise software.
Java provides a good enough mix of performance and flexibility to still be a competitive choice for large enterprises.
Because once something is created, the best language to modify or extend it is what it is written in. Java is probably 30 years old, and not too bad.
Released 1995.
Well, if we want to be pedantic here, it actually started in June 1991 under the name Oak, which this aforementioned language was initially created by James Gosling in 1989 as part of an ongoing set-top box project by Sun Microsystems, so technically speaking it's actually older than 30 years old lol!
Ha, yes. I have a copy of Wired from 1993 talking about Java only as a language for devices. So I was going to say over 30 years too, but I played safe!
i think c++ has the crown for longest very popular language