What kills me with JetBrains is they work on a barely functional (according to vim coders I talk to) simulation plugin, instead of just investing resources into integrating Neovim as a backend via plugin. You can literally have all the niceness of JetBrains IDEs with the editing power of Neovim. That alone would flip so many die hard Vim users.
I had a few people who wanted the better IDE, but they hated the keybinding hell they were going through. Having a true integration would have flipped them fully.
The problem there is that you'd be integrating two massive codebases, each with different expectations, assumptions etc. No matter how hard you try, they'd clash in places and some things would not work, leaving one side or another unhappy even with this massive effort. IdeaVim makes it work by having a massively simplified vim-like editor, specifically written for IntelliJ.
