I mean, I'd argue they are doing very different things. The Arch wiki is a collection of full topics that give you an overview of the thing as a whole. SO is a collection of q&a. I find that I need the former much more than I need the latter when it comes to managing my system, and that's probably just the nature of the task at hand. Generally I want to perform a complete task, and having a guide through that means I'm unlikely to encounter a specific problem of the type that SO is good at answering.

Also, the way in which Arch is as a system makes it less likely you have that kind of problem. Because you install and configure everything yourself, there is less 'magic' that is likely to go wrong in a way you don't know how to begin fixing it.