You asked "How often should it happen that the players look to the MC to say something, with the MC making a move in response?"You don't seem to have answered the question I asked.
I set out my thoughts as to when and why that would happen in play. I don't think there can be any doctrinaire answer as to "how often".
Look at this example from upthread:
We have two examples of the GM making a move because the player looks to them - describing the door opening, and describing the T-intersection - in what looks like about 10 or 15 minutes of play.I don't frame scenes in Apocalypse World, I make moves.
I don't know. Did I just make a move? If so, which one did I choose? What things did I consider to land on that move?
Here's one possibility:
Player: "I open the door."
MC: "It takes you a minute, as the rusty hinges won't give, but eventually you push yourself through a little crack on the door."
(Which move did I just make?: Open the way (Landscape). Why did I pick it? It supports one of my principles: Look through crosshairs. 'Dremmer sure wishes he had barred that door.')
MC: "As you walk around the complex, you arrive at this kind of T junction in a corridor. You know, like in one of those poorly designed Dungeon Modules we used to play. What do you do?"
(Which move did I just make?: Put someone in a spot. Why did I pick it? It supports one of my principles: Respond with fuckery and intermittent rewards.)
Player: "Hmmm. I think I'm going to try and Read a Sitch"
MC: "Read a Sitch? Is this situation charged?"
Player: "You bet! Who knows how long I have before someone comes down here."
MC: Makes a mental note. "Yeah, that sounds pretty charged. Roll it!"
Player: "10+! I get three questions. Where’s my best way into Dremmer's chambers?"
MC: Thinks for a second... "You notice that the floor has some muddy boot prints that go to the right."
(Which move did I just make?: Offer a guide. (Landscape) Why did I pick it? It supports one of my principles: Respond with fuckery and intermittent rewards.)
Player: "What should I be on the lookout for?"
MC: Remembers his mental note. "Someone left a 'walkie talkie' on a table nearby. Suddenly it goes off 'Basket, you there? Did you go out to piss AGAIN? You better get that pus-riddled bladder of yours checked.'"
(Which move did I just make?: Announce future badness. (They have walkies, they are on patrol, Basket could be near, they probably heard the door.) Why did I pick it? It supports one of my principles: Barf forth apocalyptica.
Look at Move Snowball on pages 152-158 of the 1st ed rulebook. It happens quite a bit:
p 152 - Marie find Isle and companions eating peaches on the roof.
p 154 - After Isle sucks up the harm from the direct-brain whisper projection, the GM describes the consequences of that and asks Marie's player whether Marie sticks around, and then when Marie says that she goes home, clarifies that she's home an hour later.
p 154 - The GM describes Keeler's gang members (Plover et al) arming themselves.
And then, because Keeler's player chooses not to impose her will on her gang (ie chooses not to trigger a player-side move), on p 155 the GM describes the gang members arriving at Keeler's house, including elaborating on the description when Marie's player declares that Marie looks through the peephole.
p 156 - Marie sets off her pain-wave projector (which isn't a player-side move). The GM describes the response of the NPCs to the harm that they suffer, and then ask Marie's player what Marie does.
p 157 - The GM describes Plover carrying out Marie's in-brain puppet strings command, just before Marie picks up the chainsaw, kills Plover, and allows Whackoff to die.
p 154 - After Isle sucks up the harm from the direct-brain whisper projection, the GM describes the consequences of that and asks Marie's player whether Marie sticks around, and then when Marie says that she goes home, clarifies that she's home an hour later.
p 154 - The GM describes Keeler's gang members (Plover et al) arming themselves.
And then, because Keeler's player chooses not to impose her will on her gang (ie chooses not to trigger a player-side move), on p 155 the GM describes the gang members arriving at Keeler's house, including elaborating on the description when Marie's player declares that Marie looks through the peephole.
p 156 - Marie sets off her pain-wave projector (which isn't a player-side move). The GM describes the response of the NPCs to the harm that they suffer, and then ask Marie's player what Marie does.
p 157 - The GM describes Plover carrying out Marie's in-brain puppet strings command, just before Marie picks up the chainsaw, kills Plover, and allows Whackoff to die.
So that's six times in what seems like it would be about half-an-hour, or maybe a bit more, of play. Which is actually a similar ratio to @andreszarta's example, although I don't want to make too much out of what is probably a bit of a coincidence.
So my answer is as often as makes sense - but every ten minutes or so doesn't seem out-of-kilter with the examples I've analysed. I know @chaochou suggested less often, but I don't know if he would count all the examples that I've identified as instances of what he was counting in his answer to you. Because he seemed to be thinking of examples where there's a lull in the action and the GM offers a bit of redirection or a jump-start: whereas I'm also counting examples that occur in the midst of the action.