Writing Scala with IntelliJ is just so fun - 99% of time I get the right suggestion for Scala and/or Java libraries that I have not imported yet.
Nice style suggestions that do not nag. Instant ScalaDoc generation. Pretty much picks up on all my brain farts.
I imagine it is because of deep integration with JVM - after all IntelliJ started with Java.
By comparison VS Code is just an editor underneath without the I in IDE.
Theoretically VS Code is a bit like emacs or vim, you can set it up to do everything for your language but it takes a lot of tweaking.