Yes, there are supposed to be reasons in the imagined world. But those reasons don't affect the roll; and the game can be played without ever actually settling on what those reasons are.
In "new-simulationism" setting design precedes abstraction design. Outside of play when the abstractions are formed an earnest attempt is made to ensure that the roll will represent setting at the point of play. The abstraction that "dim light" can make surprise more likely in D&D is one example.
And of course every RPG supposes that there are reasons in the fiction to explain whatever is imagined by the participants. So this can't be enough to satisfy the manifesto's demands.
But there are no representations. The roll for surprise in D&D is not a representation of anything. It is a process for randomly deciding whether to narrate <this> - a fiction where the characters are aware of their surroundings - or <that> - a fiction where, for some reason that the process doesn't itself determine, the characters are distracted.
I reiterate that this is true of all resolution systems in all RPGs. So if this satisfies the manifesto, then all RPGs satisfy the manifesto. But clearly that's not what its author intended.
The over-productivity you identify looks thorny to address. My first thought was that analyzing principles in isolation doesn't seem right: they should be read together as a whole. Setting precedes abstraction precedes play. The abstractions have setting as their target reference and per 9. that cannot be perfectly simulated. At the point of play, principle 3. demands that GM fill in needed details faithful to the same reference. So that first line of principle 4. works together with other principles and should be assessed on that basis.
The surprise abstraction represents that creatures in the imagined setting can be caught flat-footed, especially in dim light, and when they are they are often slower to act. GM has the job of evoking the rule when circumstances in the fiction match circumstances of the right sort in the imagined setting, including reasons felt significant enough in the setting that the abstraction captures them, such as dim light, with consequences of the sort imagined to be typically seen in the setting.
But what you say makes it very noticeable that principle 4. and "new-simulationism" overall isn't prescriptive as to available forms and methods of abstraction. For example, it doesn't differentiate between simple-fail and fail-forward: either is fine, just so long as they can be used to represent setting. It only rules out abstractions that represent anything other than the reference setting that precedes them. To my reading, principles like 6. even lean it toward an FKR appreciation of how that should work out.
That notwithstanding, Sorensen's principle appears to rule out some other RPGs through exclusion of the things that they want to do. As is reinforced by "and nothing more." It's not the job of "new-simulationism" abstractions to introduce the unwelcome and unwanted to the fiction so if the thing an RPG wants to do is that, it's ruled out. It's not their job to ensure the fitness of characters, put them in conflict, drive passionate reactions, so if the thing an RPG wants to do is "narrativism", that's excluded. It's not their job to hide information and demand players make commitments before seeing the outcome, so "guess and script" is ruled out.
It's only their job to make the imagined details and dynamics of the imagined world available to play. That leaves open another route to over-productivity, which is what happens if the world I settle on is one where passionate, fit characters conflict? Couldn't the tools for anything that some RPG could do, be built into the world itself. I suspect that has to be accepted so long as it is that world and no other that the abstractions represent.