Why did C++ survive the advent of Java? One reason: the mainstream JVM, HotSpot, is written in C++. As such, the production Java ecosystem is not self-hosting and relies on C++ to be sustained.
(Writing a JVM in just Java is doable, and some research JVMs have done it, but that approach hasn’t yet been fully productionised.)
There are probably >100,000 c++ devs out there, and ~100 of them work on HotSpot. I don't think the HotSpot devs are significant in encouraging c++ usage
I think it demonstrates the point - that if Java is not able to be fully self-hosting in practice, then there are significant gaps in its abilities – and those same gaps in its abilities that drove HotSpot devs to implement HotSpot itself in C++ instead of Java also drive other projects to choose C++ over Java.
(Writing a JVM in just Java is doable, and some research JVMs have done it, but that approach hasn’t yet been fully productionised.)