Why, then, is it an exception to that when a player introduces some open-ended gameplay due to a class feature they want to use? What's the difference between using the command spell to tell someone standing next to a window to "defenestrate" and shoving that same NPC out of a window, or a PC using acid to dissolve the hinges on a locked door, or a PC offering to cook a meal for the banquet and giving everyone food poisoning? Why is the former a bigger burden, when we are asked to do this same task as a DM, over and over and over again, in many other situations?
I know I said I was out, but, this is a very good question and doesn't rely on calling anyone a bad actor.
The difference to me is very clear. In your example of shoving someone out the window, the player is engaging the game, not manipulating the game rules to get a result. Same with all your other examples. In the Command example, the player is not using the game at all. They are abusing the vagueness in the description of the spell so they can gain extra utiity out of the spell that was never really intended.
Note, this isn't just about the Command spell. It's that the player does this over and over again with spell after spell - attempting to abuse the open ended nature of the poorly written mechanics in order to "win" the game.
In your other examples, there are clearly written, not at all vague mechanics for resolving them - to defenestrate someoen, you need to push them (or grapple and move them, whatever) out the window. To pour acid on the hinges, you actually need to have acid. To poison the meal, you actually have to have poison, or enough cooking skills to be able to do it.
IOW, at no point is the player manipulating the rules of the game to gain an advantage. They are directly interacting with the game world.
I get that some people don't see a difference here. To me there's a world of difference. When the players are manipulating the rules of the game, it's ... well... meta-gaming. It's not engaging with the in game fiction at all.