This all makes it apparent that what you think I am saying, and what I am saying, are somewhat at odds. I am aiming to look closely at individual rules. Not procedures or mechanics made up of rules. I am not trying to say how rules ought to be deployed, I'm aiming to say what they are.
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In the above I don't mean to say that I have the right or best grasp of anything, but principally to point out that your and my concerns are very different. Mine are ontological, as I said. What are rules?
There is an extensive literature on what rules are. The literature I'm pretty familiar with goes back to Kant, but there is obviously a literature that predates that which goes back at least to Plato. And that's without having regard to literature in non-Plato influenced traditions, in which I'm less well educated and so which I am less confident to comment on.
Framing "what are rules?" as an ontological inquiry is fraught. Wittgenstein spilled much ink arguing that this is misguided, and that the proper question is something like "What does it mean for a practice to exemplify a rule?"
Some scholars think there is utility in comparing rules across domains of human activity (eg Marmor thinks games and law can both be looked at via the relationship between rules and conventions). Others have doubts.
Here's a rule of law from the Australian Criminal Code: "A person commits an offence if the person engages in a terrorist act. Penalty: Imprisonment for life."
Here's a rule of law from the Victorian Crimes Act: "A person must not, without lawful excuse, intentionally cause serious injury to another
person in circumstances of gross violence. Penalty: Level 3 imprisonment (20 years maximum)."
Each of these two rules has a different syntax: the first is a conditional definition of a particular offence. The second is a statement of a prohibition.
Neither instantiates the general form you have suggested, of extrapolating a consequence from a description. (One could insist that your form is the general one, and that these rules
really have the logical form you've set out. That would require argument.)
Nor does either of these rules rest upon the rule/norm contrast you have deployed. The second, at least, seems amenable to analysis by reference to Finnis's account of the precisifying function of some legal rules. More generally, what the "ontology" of these rules are is something that is hotly debated among (inter alia) legal positivists and anti-positivists. And of course there are also scholars who argue that those "ontological" debates are meaningless or pointless.
In any event, I don't think we need to engage in these sorts of arguments - about the nature of rules; their general form, syntax and sense; their ontology or "grounding"; etc - in order to talk about RPGing.
If one reads the OP as asking
Why do players of RPGs deploy normative standards for their play - which is a voluntary activity - beyond sheer socially-negotiated agreement, one will have understood the question fine and be in a position to address it.