If your OS was written in Java...
God forbid, if there were such an atrocity it's boot time would measured in days
Besides, I'm pretty sure Java run-times are written in C/C++ so you will have that on your system anyway.
...the suggestion is the best language might be Java
I think Java is a bad example but, yes, I do get your point.
So regardless of any technical merit other languages might have, the "system" language has certain "practical" benefits. It is often the best language when you just want to "get the job done".
For many applications C offers a lot of resistance.
Memory in C++ is a leaky abstraction .