I'm A Banana
Potassium-Rich
It doesn't necessarily follow that because D&D has no game theory win conditions, this yields a DM whose job it is to simply facilitate others' enjoyment. In fact, it isn't always strictly true that D&D has no game theory win conditions, though it certainly has that potential.Because DMs are not playing a game, in the traditional sense.
DMs do not have a game theory win condition. They do not have a game theory lose condition. Their role is to facilitate the enjoyment of the game - and, I would suggest, they are primarily there to facilitate the players' enjoyment of the game.
As a DM, your goal should be to derive enjoyment through your players' enjoyment of the game. In my eyes, you're not a good DM until you've gotten there. Any argument along the lines of, "If I wanted to control everything I'd just write fiction," misses the point on two counts - first, it ignores the fact that the DM doesn't control the players, and can therefore be surprised by their decisions even while maintaining control over the game world; second, it completely sidelines the players' investment in the game by holding that the only important difference between playing D&D and writing fiction is whether or not you can surprise the DM.
Facilitating the enjoyment of the players doesn't necessitate establishing strict control. It is possible for players to enjoy randomness. In fact, given the nature of surprise and excitement, it is more likely that a player will enjoy randomness far more than they would enjoy control.
You're right that a DM doesn't control the players, and can be surprised by them. However, part of what this means is that a DM cannot reliably foreknow such things as what creatures will be fought in combat, and what creatures will be parleyed with, or where the party may travel. A strongly narrative DM may be able to make fairly strong educated guesses, but not every group enjoys a strongly narrative structure on their game experience.
Furthermore, postulating that more enjoyment results for some people from a lack of control doesn't by any stretch mean that it is the only important difference between a narrative and a D&D game, it simply indicates that it is one important difference.
I realize that this is a nuanced position - it makes an effort to acknowledge things like the difference between the game world and the players' sphere of control, the fact that the players have their own hedonistic calculus to satisfy, and the fact that random encounter tables are designed as a tool of convenience rather than a formula to construct an ideal game around - but dammit, it's about time we started trading in nuanced positions instead of, "Embrace the chaos!"
Your position isn't the only nuanced one in the thread, and you'd get much more out of this dialogue if you perhaps tried to discover the nuances of others' positions instead of relying on condescension to shut down opposition.