Java is actually not that bad – Java with LWJGL gets you within a factor of 1.6 to C++ performance, while actually being "write once run everywhere" (for PC, at least). That’s good enough.
You're not allowed to do JIT on consoles or mobile and you're memory constrained. A PC-only game engine is going to be a tough sell these days.
Also, unless you're bundling a JVM (not sure about the legals here) you have to make your Windows (i.e. primary) customers install the obnoxious Oracle Java runtime.