It applies to more than just language design too. Why do I love Emacs so much? It isn't the idiosyncratic terminology or weird keybindings, it's the fact that Emacs is an editor that grows. Once I understood basic Elisp, there was no real friction to take Emacs and start molding it to exactly my needs and preferences. Something I don't like? Something that's missing? I don't have to spend hours setting up a plugin to fix it; chances are it will only take a few lines to change whatever I want to change, and I can use Emacs's remarkable discovery features to quickly find which lines those are.
Why do people swear by command-line invocations and bash? Bash is awful. But it's an environment that grows in a way that I've never seen with GUI apps. A small set of simple tools and a universal way to compose them is remarkably powerful, even if it's as awkward and error-prone as POSIX shell scripting.
Excel? I don't use it myself, but I've seen the same thing from Excel power users: it goes beyond mere calculations to letting people seamlessly build what they need on top of Excel. Excel is integral to the modern world in a way that no other pieces of office software is because it can grow to solve complex problems in a way other tools can't. (With, as I've seen working at a large company, occasionally terrifying consequences.)
What I would really love to see next is an alternative to Jupyter that can grow in the same way. Maybe gtoolkit[1] is a candidate? That's what I'm exploring now, and it's pretty exciting so far.