I've been using vim for roughly half my life at this point. What I've found is that actually using the editor is so thoroughly muscle memory at this point that using another editor, where I actually have to consciously think about how to do something, is incredibly distracting.
It's not like the difference in input speed is really meaningful; as you'll see someone point out in any discussion about this stuff, the bottleneck in programming is thinking.
But what I find will often happen is:
1. I settle on a course of action.
2. I go to actually do it.
3. The editor doesn't do what I expect, because it's not vim.
4. I am momentarily confused, and have to think for a minute about how to do what I want.
5. I lose my train of thought entirely.
6. Rinse, repeat.
So for me it's not so much about any specific thing the editor does to make me productive. I do have opinions about some things, but what's important is that it just fades into the background and lets me think about the problem I'm trying to solve.
Beyond just being "different," I tend to eschew IDEs for much the same reason -- while many of the advanced features seem useful, I find them too distracting to be worth the trouble. Just me and the code, please.
I worked at an automotive shop for a while. Let's go with an impact wrench for an example.
In the car shop world, impact wrenches are primarily used for the installation and removal of wheels on vehicles.
The impact wrench I started with had a single internal hammer- the thing that makes a click noise and applies torque. After a while of using it, I could hear when the wheel was seated correctly, and when it wasn't.
Later, that tool broke, and got replaced with a dual-hammer one- and all of a sudden, I couldn't hear-- feel-- when wheels were on right, and it took me a few vehicles to adjust to the new noise, weight, and feel of the tool. I got used to the new one eventually, but I still liked the noises that the original wrench made more.
Before I adjusted, I was unable to perform that part my job correctly because I didn't know exactly how to use the new thing that was identical in use-case to the old one.
My CAD program of choice doesn't have many keybinds stock- and so I've bound my own shortcuts to different things buried under various menus. I also have a Logitech G502, which has buttons on the sides of it, that I've also bound to some of the more-used, harder-to-get-to functions. It's much easier to open up the parameters table- which I use heavily to tweak designs I make. It's the way I like to do things, and that one bind on the side of my mouse saves me from rooting through menus all the time trying to find the same thing over and over again. I set up that bind almost two years ago, and I've been using it ever since.
When I got a new laptop recently, I had a hard time doing CAD until after I ported over all my keybinds and stuff.
Now to answer your question- because those of us who use powerful tools to build custom stuff also like to customize the tools we have for the task at hand. A developer who's used to their setup that they live with every day will undoubtedly have a hard time using the factory settings, and an even harder time working with someone else's bindings.
Why do people become so dependent on tools? Because we mold them to suit our desires, and they become an extension of who we are, and what we can do.
How did you become unable to do basic text editing without a specific editor setup? Why do people become so dependent on tools?