It's not a miracle but rather a testament to how much Neovim improves upon Vim. The number of useful features, among them Tree-Sitter and LSP, that Neovim has introduced has ended what feels like decades of stagnation in Vim development.
Now imagine an editor like Neovim, but instead of working through 30 years of cruft and legacy code, it's built from the start using modern software engineering techniques and incorporates such features into its core editing model. That's essentially what Helix is. The Vim -> Neovim improvement is nothing compared to what Helix will deliver (and already is delivering in many aspects).
User inertia is strong. Neovim has its success because of its improvement, but more importantly, the keymap and config language is based on Vim7. Vim7 users can painlessly switch to Neovim with all config preserved. That's the main reason why Neovim can gain a large number of users initially. Conversely, Helix has no keymap nor configuration compatibility with Vim or other mainstream editors. Given this, I see no hope that Helix will become mainstream.
My vimrc already has a bunch of configuration in it, I'll give Helix a try when it is able to parse that (so, probably never, I guess).
I hope this doesn't come off as flippant: I thought your comment was sarcastic at first.
While I love seeing newer / better software displacing the old and crusty, this seems a little unlikely, no? It seems like somewhat of a miracle that neovim has taken as much share as it has.
P.s. I'm hoping to eat my words one day.