Yes you are right its not that easy and also it would need testing.Options are nice. But, I think the core game should be balanced before we get 'pages and pages' of options. It would be less efficient if everyone was manipulating tons of options and then discussing their gameplay and devs trying to balance the game based on the widely varied play experiences.
It's also not as simple as just mapping the XML values to the GUI. There are going to be bugs associated with the actual options you pass through that you cannot anticipate. So they will need to be tested. And, each time you make changes to the game- they are going to have to be all tested again. It will cause delays.
Just as an example, the new speed settings cause occasional animation glitches. If you set the zombies to 'run' - they glitch out occasionally and warp around after playing their pain animation but before continuing the run animation. That's an option they put in the game born from an existing variable just as if they had provided it for you to change manually in the game's GUI. Even when they actually did it themselves - it's STILL got bugs..Imagine the bugs if they just linked the XML to an options page in the GUI and let you go hog-wild changing things.
But they coudl stop removing more and more Stuff from the game to force people to play with new skill system to force people to use the dumbed down crafting and such stuff. They could simply keep the old Code and Functions and let the User or Modder decide if he want to use the new Skill system or the old System, if he want to use the new Crafting or the old Crafting (i dont talk about the crafting grid ) .
Also there wold be no need for the Pimps to support people who play with Mods if there is a Bug or Issue which is not a regular Game Bug.
And really i dont need 10 Pages of Options would be fine if they are in the UI would make things easier , but i hate that i cannot as example bring back weapon crafting with parts quality cause the Game does not allow it anymore also not after i bring back weapon Parts. and i dont think it would need months of testing to not remove the function to use crafting by part quality . How the modder add this to his mod is nothing the pimps must test or bugfix as long as the pimps dont remove the needed Gamecode.