Because that's not how GMing works, even in PbtA. And also because a GM can pick the most logical option and still make the story interesting.
Also, that's right. You probably wouldn't pick the cloak unless it had sentimental value. Or they were in an area with terrible weather and needed a warm cloak in order to not freeze or get soaked. If the cloak was otherwise meaningless, you'd pick something else, such as the orc getting a free blow in (the GM's "deal damage" move), or Brog not being able to prevent all of the Badness from escaping.
This is how an orc is written in DW:
Orc Bloodwarrior
Horde, Intelligent, Organized
Jagged blade (d6+2 damage, 1 piercing); 3 HP; 0 Armor; Close, Messy
The orcish horde is a savage, bloodthirsty, and hateful collection of tribes. There are myths and stories that tell of the origin of their rage—a demon curse, a homeland destroyed, elven magic gone wrong—but the truth has been lost to time. Every able orc, be it man or woman, child or elder, swears fealty to the warchief and their tribe and bears the jagged blade of a bloodwarrior. Men are trained to fight and kill—orcs are born to it. Instinct: To fight
- Fight with abandon
- Revel in destruction
Orc Berserker
Solitary, Large Divine, Intelligent, Organized
Cleaver (d10+5 damage); 20 HP; 0 Armor; Close, Reach
Special Qualities: Mutations
Stained in the unholy ritual of Anointing By The Night’s Blood, some warriors of the horde rise to a kind of twisted knighthood. They trade their sanity for this honor, stepping halfway into a world of swirling madness. This makes berserkers the greatest of their tribe, though as time passes, the chaos spreads. The rare berserker that lives more than a few years becomes horrible and twisted, growing horns or an extra arm with which to grasp the iron cleavers they favor in battle. Instinct: To rage
- Fly into a frenzy
- Unleash chaos
Those last two things in each statblock, the bulleted list, are the orc's moves. (You'll notice that they don't have any rolls attached to them. GMs don't roll.) Thus, a GM who is running an orc bloodwarrior or berserker would use the orc's moves--they would make the orc act in ways that allow it to fight with abandon and revel in destruction.
As I said before, the introduction of a kitten has nothing to do with the action of
Brog moving past the orc. Therefore, it is not a legitimate complication to rolling low on Defy Danger. Now, you can establish that the orc has a bag of kittens and is yeeting them all over the place to get in the way. But that's the
orc move Revel In Destruction or Unleash Chaos,
not the result of Brog's move.