Then (honest question) why are they game masters? That's part of GMing: picking what rules to engage and how.
Because maybe they are good at the other parts of GMing, and they and their group don't really mind the occasional fudge.
Remember, if everyone's having a good time at their table, that is all that matters. Failing to meet your concept of what is proper or good for everyone isn't a real issue.
What's an example of "Content" in this context that isn't "rules"? Like if you chose a monster that's too powerful then you essentially chose a set of numbers that are too high.
As one possible example, yes. But, that choice was not necessarily governed by a rule that can be changed. Many games don't have a concept of rules for such. The guidelines D&D gives in various editions are all flawed, and nobody, including the designers, have been able to make them universally "fixed"
Why are you positing only those two options (both of which have obvious downsides)?
For two reasons: I only need a couple to prove the point that reasons exist. That's all I was aiming to do.
As soon as it happens even one time, the players are always aware it could happen again.
Not in practice, no. Yes, they are disincentivized if they figure out when and how they can rely on it happening. But rare, unpredictable fudging doesn't have that result.
They don't have to predict when a fudge us coming, they just have to feel that there are sometimes outcomes the GM will force and that makes their choices matter that much less.
Again, that's not what happens in practice at the appropriate table. If the players are not really terribly stuck on the idea of challenging themselves against an objective ruleset, they wind up not caring.
Once you know a GM is capable of fudging, you know you don't ALWAYS have to try as hard as you can.
Again (and perhaps the last time) no. If you cannot predict, then you still have to try. You can only slack off trying when you know the fudge is coming - do it any other time and you hose yourself.
My proposal was:
Assuming the change has no cost at all (in time or effort) why not change the rule and close the loophole?
That certainly isn't how you worded it before.
Yeah, so to ask the same question a third or fourth time:
Why not play (say) FATE then?
As I said already - because the given ruleset may present appropriate results the overwhelming majority of the time on its own. Many feel you don't need to change to an different ruleset for an edge case here or there.