Java has its faults, but it's a higher level language than C++, and that lets people write code in it more quickly.
Memory management is a huge problem pushing performance. You can still write efficient Java by doing things like no newing of object in ticks and stack arrays but gamedev is heavy in management of memory access/organization, stack vs heap allocation and other things that take lots of work or are too hard to control in Java or other GC platforms (C#). Though there were a ton more XNA games (C#) than Java even today but that has since been discontinued. Windows Phone 7 also limited its potential due to no native access and requiring XNA only games. Android didn't really take off in games until the NDK in Android 2.3 which was deemed a game developers OS. iOS had it right since the first SDK allowing C/C++ and Objective-C or Objective-C++ which allows mixed that I have seen in all custom engines for iPhone.
It's just unnecessary. You can write "safe" C and C++, you just have to know what you are doing to begin with. Also, don't forget about the massive amount of native frameworks that have been developed already. Why rewrite an engine which already exists just so you can use Java?