Because anything else would not be AnCap, by definition. It may call itself that, but it would not be. Much like the current United States insists upon calling itself a Democratic Republic, though it abandoned those principles some 150 years ago.
You seriously insult me if you think that is an answer. Let me ask the question again. In your AnCap system, which I will allow you the unrealistic supposition that NAP is the law everywhere, how is it that NAP will remain the law, and not mutate into various versions of SSOLWADNNAP, depending on locale or region?
Or, in a more realistic hypothetical world, however did NAP become the law, when it is in competition with various versions of SSOLWADNNAP?