I had tinkered with emacs over the years but mostly used vim for programming, until the past year or so when I started writing Haskell and LaTeX for school and put in a determined effort to use Emacs full time. I've found I like a 'regular' text editor more than vi's modes, and that (like rickdale's comment) when I've tried out other editors like Textmate or Sublime Text, they feel like they're missing something compared to the raw extensibility of Emacs. (What that something is I'm not quite sure and - I just feel like if I want an extensible editor, emacs is the best. Strong opinion weakly held I guess)
My advice to new users is to start simple and try to only add in extensions/modifications when you hit pain points. I added some universally useful/specific ones early on like AuCTeX, a solarized theme, turning on syntax highlighting, haskell-mode, and so on, but I've found that piling on a ton of plugins and getting away from the 'default' behavior makes it much harder to create a comfortable workflow. This is also why I'm not a fan of stuff like Prelude or emacs-starter-kit.
I think it depends on what people are using their editor for whether they'll jump ship. I started out on vim, and I really loved it. Then I was typing up papers using the vim latex suite and syntax highlighting would cause my machine to choke every time I scrolled through text. I could have just turned off syntax highlighting, but I tried emacs and auctex, and it worked wonderfully. Since then, I found a bunch of other things that I prefer about it, and only really use vim for quick config file edits. Now that I've been playing with it for a while, chords are second nature, just like modal editing became for me with vim.
I imagine that nobody who's terribly accustomed to either editor will switch unless they've got a specific need their current editor doesn't meet.
I had a similar experience, really. Do I want to use emacs to edit system files and such? Not really, I'll continue to use vim. But for programming projects and document writing I like emacs better. To be honest I think the thing that started it was messing with Sublime Text; after using it for a few weeks I started tinkering with emacs again and never looked back. I will say that I never fully bought into vim in terms of movement keys and in depth shortcuts; I pretty much used cursor keys and the mouse and didn't do anything too advanced.
I actually started using Emacs at work when work became dangerously boring and I was looking for a distraction. Plus I had read a lot about Emacs in my Vim days and wanted to know what it was all about.
So I suppose I actually switched without a specific need except for curiosity and boredom. I'm glad I did though, since Emacs has improved my life quite a bit since then.
I use both Vim and Emacs, and in most contexts Evil-Mode within Emacs that emulates most of Vim's vanilla functions.
Emacs also has modal editing that allows for per mode based keybindings.
Where Vim wins out though on the keybinding game is with its grammar that enables a great deal of mnemonics and the ability to bind keys based on key sequences that do not all have to be prefix keys except for the last key in the sequence, which is the case with Emacs currently.
That opens up a lot more options for generating terse keybinds that are simply not possible with the way Emacs binding system currently works, and coming from Vim I found the system extremely confusing until I read how Emacs keymaps lookups work in greater detail.
That spills over into what is possible with Evil-Mode bindings as well to a degree because of the prefix key requirement with the sequences.
And in Emacs, because of its keymap hierarchy system it is extremely easy to have custom keymaps shadowed and overruled by a higher ranking mode mapping, which again coming from Vim is not obvious what is happening there and how to overcome that behavior.
Even though I now grok how Emacs processes keymaps, I still much prefer Vim's system that allows for any key sequences to be interleaved to make very terse sequences.
The workaround to the situation with long chord sequences that use the Meta and Control keys is that I will bind the frequently used command to the hyper or super keys which are largely not used by modes nowadays and are much less crowded as a result.
There is no inherent reason why Emacs could not move towards a key sequence rather than a chord sequence binding scheme, so resolving the quagmire is at least tractable.
I do use Emacs chords where they are reasonable though rather than changing states just to interact with a REPL or a VCS mode, and in the context of working with Lisp I always use Emacs' chords as paredit obviates the need for any of Vim's grammar, which by default lacks a sexp object or ways of transposing objects well.
My advice to new users is to start simple and try to only add in extensions/modifications when you hit pain points. I added some universally useful/specific ones early on like AuCTeX, a solarized theme, turning on syntax highlighting, haskell-mode, and so on, but I've found that piling on a ton of plugins and getting away from the 'default' behavior makes it much harder to create a comfortable workflow. This is also why I'm not a fan of stuff like Prelude or emacs-starter-kit.