They rewrote it (not sure if in C++ or C#) for the windows store and it works perfectly on computers that can barely run the Java version.
Microsoft rewrote it because they're not a Java shop. Microsoft Games Studio not only uses C#, but their mission is to increase adoption throughout the industry as it feeds into Microsoft's ecosystem. Microsoft is about developer mindshare.
C# and Java are incredibly similar languages. They're almost indistinguishable. Pointing to C# as if it's substantially different from Java makes me think you've never used either.
C# is much faster than Java. Comparing them in real life performance situations (and not synthetic benchmarks) is almost a joke.
Source: have been doing low-latency engineering for over 15 years.
It's quite apparent your experience with Java language/runtime is outdated and/or shallow. Maybe try reading up on it before making strongly opinionated comments like this?
I don't mean to over hype the issue, minecraft became on of the most successful games in history riding on Java. But the re-write to C++ was not just because Microsoft is a C++ shop. The C++ rewrite delivered measurable performance gains, making it much better on low end devices especially.