“Does Java2D run on Metal?” doesn't seem like a top 10,000 question for Apple. It does however seem like a top 10 question for JetBrains. And so here we are.
They don’t want to be running around making Swing and SWT and Qt and Gtk work well on macOS. They offer their own and you can take it or leave it. I guess this lets them simplify and focus. It obviously works for them.