"I'm honestly confused at how much effort people spend on .vimrc and .emacs files to get poor versions of narrow slices of functionality that comes out of the box with the most basic of IDEs."

I think that it's the other way around: people don't want to lose the editing experience that they already have by switching to another environment that might have some other benefits. For some people, that means an environment that they've tuned to their own requirements over years, and for others, it's just the core interaction model.

For me, I like modal editing, and the Vim commands are now automatic, but I have no attachment to any implementation of these, so I use the stock Vim on CLI, and VS Code with the Vim extension everywhere else to get modern features without losing the aspects of Vim that I really care about.