I presume you either really don't like Java or simply are not aware of what Java is in the development environment. Personally I'm not too fond of Java - it's too verbose for me and annoys me.... but that doesn't change the fact, that most of the community games are written in Java or Java/Erlang. And those games are currently a larger market than traditional ones. So saying that Java game dev community is tiny is... somewhat misinformed.
If you compare Java to C++ - it's not that slower, especially if you go for cold, hard calculations, that are being repeated multiple times. JVM does miracles with optimization and sometimes Java simply blows C++ out of the water. And it doesn't matter if Oracle cares about games - languages are not made to support games, but to support features, that games also use. So argument about Oracle is somewhat misguided. Same with garbage collector - doesn't matter - Java is garbage collected and does clear resources pretty well. More useful would be direct control over memory and pointers, than GC.
As for higher/lower level languages - Java is as high/low level as C++. C++ is implemented in C. Java is in JVM's code. While your argument is somewhat valid, it all depends on implementation. For example: EVE is written in Python (or well - their own implementation of Python), which is high level language written in C. And to be fair - it handles 1000+ players battle better than WoW ever handled 80 people battle. And if you go on the language levels - there's for example Go (written in C) that destroys most of other languages in terms of efficiency. It even beats C when concurrency steps in (hello online games), because it's implemented so well.
Speaking of platforms - Java works everywhere, where JVM works. So... windows, OSX, Unix (including Android) - and that makes up for.... umm all of used languages? And with some small effort (usage of env vars etc) you can have one code, that will work on each platform without rewriting.
To summarise - while Java might not be perfect to write games like WoW, it surely would do a decent work to run stuff like card game, because there are 35495893865 similar games in Java already there and working with communities around them. And while C/C++ is excellent language and widely used for clients/servers, there are times where it's not best - Erlang blows it out of the water for server side computing for example.