I mean, that's more or less the reason why it isn't Java, not why it's ultimately C#. My guess is that Java is just what they're most comfortable with, with C# being similar enough but avoiding specific limitations in that case.
I think my question is why not choose c# for this? What’s the apprehension here if any?
Wasn't C# essentially microsoft throwing their hat in the ring against Oracle and to show off how cool this .net stuff is?
I dabbled in both at around the same time a long time ago for console apps and visual studio's autocomplete / assist / library fetch etc made it easier than Java to get working in but...
Its been so long I forget the origin stories sometimes.