Why would writing a patch for any other editor be easier (or less hard) than writing a patch for Emacs?

Emacs API is just insane with too many special cases or with other packages unexpectedly affecting semantics. Even after stepping in debugger I often could not be sure if the things worked like I thought they should work with too much unstructured global state that is randomly poked.

I use Emacs since about five years straight, every day, and have used it on and off before, and have quite some Elisp in my .emacs.d, and can say that you're totally wrong on this. Yes the language has problems, the API, having been there since many decades ago, has quirks, but not more than most of the common languages out there, JS, C/C++, Python, Ruby, Perl, what not. What modifies the global state (mark, match, etc.) is well defined, and you can avoid learning it unless you're sending patches or maintaining your own packages. And dealing with programming languages' idiosyncacies is our raison d'etre anyways.

That doesn't quite ring any bell.. Have you used edebug? I haven't seen that level of code introspection and debbugability in any other tool, even a development environment.

Emacs allows you to look into and debug any function or variable, be it internal that shipped with its core, or one that you wrote.

In any other program, such customization you made would be impossible.

The things you can customize in other editors and IDEs, you can customize through the M-x customize interface. The things you'd install as plugins, you can get from Emacs package manager. All other things that you can - with smaller or greater amount of work - alter in elisp, are more-less impossible in other editors.

Think about why one needs a sofisticated customization in an editor. It implies it's defaults reflecting the workflow of the developers are significantly different from yours. To fix this you essentially must become a developer. And since the feature you want is not what the developers want, your has to maintain the feature as long as you use the editor. Now think about all the time one spends on that. If it does not feel like fun or hobby, then one better try to find some other editor that matches what one wants by default or after 5 minutes of poking in the preferences menu.

Anybody can use any tool to their liking, obviously. But again, you are objectively wrong with Emacs. Every programmer has certain things they need to automate, certain recurrent tasks and then certain non-programming stuff. I am not a professional ptogrammer, and I use Emacs for a handful of non programming tasks. I do tens of things daily with it that is plain impossible with a preferences menu, and impossible or prohibitively hard to do with other programs.

Edit: Now I'm on the computer, I can link you to my init.el [1] so that you can skim and observe how much is configuration and how much is stuff that's possibly unique to my workflow. And how much is very useful stuff only possible in Emacs (one of my favourites is the URL routing stuff, at line 3674, something I inadvertently use tens of times a day).

[1] https://github.com/cadadr/configuration/blob/6a1e400488839b7...