Because the bulk of it simply seemed to be in agreement with what I'd said all along: you do what you do because you feel like doing it, and you avoid what you avoid because you feel like avoiding it. In other words, there are no actual limits. If ever you felt like railroading in a game would add something to it, you'd do it, no? The only limit is "I don't feel like crossing that line right now."
Mostly? I'll be honest: I didn't fully read the final part of the post, because I'd gotten 3/4 through it and found nothing meriting a response. That is harsh, I admit, but...it's how I felt. I skimmed over the last bit which, unfortunately, really was the meat and potatoes and is what I should have read. So I apologize for not fully reading everything you wrote. That was a bad choice. If I may correct that error now:
That has certainly been one component of it, yes. And thus, in the spirit of the above apology, I accept yours as well, even if it was only implied.
But there is a bigger component, which is not mentioned among the things you've said here. That component is that you--and others--have not only insisted that this is a way to do sandbox-y play. Rather, that it is the best way to do so, and that other systems not only are not as good, they actually interfere with or prevent sandbox-y play. Back when the discussion was about prep stuff, regarding comments from Hussar, that very much was what several people directly and explicitly claimed. Not just that collaborative creation, or GM-less games, or games with rules that apply to the GM as well as to players, are a different kind of sandbox-y play (which would be objectively correct, they are!); not just that there are differences (again, objectively correct); but that this is the highest form of sandbox-y play.
The things you keep calling "bickering" or trivialities etc. aren't trivialities to me. They're extremely important. So when someone tells me there are restrictions on the GM's freedom, restrictions beyond what the GM feels like doing, I want to know what those are. Those are of nearly indescribable importance, because they shape nearly everything about the play-experience. They set boundaries. They mark what cannot be touched--e.g. the bit a fair ways upthread where some folks almost seemed taken aback to consider that "The GM must respect what the player rolls" is a binding GM restriction. When someone says they are guided by "principles", I want to know what those principles are, because that's how they and I get on the same page. When someone says they have "guidelines", I need to know what those guidelines are so I can know where I'm being guided to. Etc.
Hence I've pressed--for clarity, for specificity, against vagueness, against passing-the-buck. And it seems that now, at last...we've ended up where I started from the beginning. As argued above, the restriction is, "Because the DM feels like it would make a better experience." Nothing more, nothing less. And I don't take that very seriously as a "restriction".
What would satisfy me would be either...
(A) When one says one has "principles" or "guidelines" etc., talking about what they are, rather than just using a single high-abstraction word. Even if you can't bring to mind any specific words, talk about what you do! Give me an actual-play example with or without the details filed off (I respect your players' privacy) that walks through your reasoning and where important principles applied, or invent one. (Both things I have personally done in this thread.)
...or...
(B) Recognize that the "principle" is literally just gut feeling. If that's actually all it is, just say that, rather than throwing up words like "realism" and "consistency" and "plausibility" etc. as though it truly did have a structured, philosophical underpinning that is somehow ineffable. It's perfectly fine to just say "I do what feels right", if that is in fact what you do. That recognizes that there really isn't any particular pattern or rubric or principle or guideline etc., it's just following gut instinct where it leads. Nothing wrong with using intuition in a leisure-time exercise....if we recognize it as intuition, and not as a procedure or principle that can be discussed. (Not something I personally have done in this thread, since...that's not what I do. But if it were, I'd say so; e.g. if the conversation were about how I balance custom moves in DW, I really do kinda just do that by intuition, on the basis of the loose statistical spread of results I've seen in play, and then tweak it later if it falls short in one way or another.)