The above responses are basically "Well, just tell them what they want to hear so you can move on to more interesting things." I'd love to. But in some cases, you CAN'T. I'm not talking about an interest in the maelstrom as flavor. I'm talking about interest in the maelstrom as the game.
Except, that never happened in the game. It was most definitely an interest in the maelstrom as flavor.
The problem was, the maelstrom was never opened up to the players to inject some of their ideas as to what it was. There was never any questions asked about how they interact with the maelstrom, or what the maelstrom meant to them. This is what my character was pursuing. Not, "what is the maelstrom?", but, "what is the maelstrom
to me?" And, it made sense. My character had a weird+3.
Unfortunately, the maelstrom was predetermined by the MC, you, to be some sort of background thing going on in the world. There were often comments during the game like, "You guys don't realize what the maelstrom is yet..." and so on. Really? Well, what is it? Either tell us or let us tell you. Never happened.
Instead, we were met with the Elminster of Apocalypse World, a 20th Level Wizard named Colt who could teleport at-will (back to her bunker by shooting herself in the face), never die because of her "clones" and lived in a bunker that was essentially a wizard's tower that only she could navigate, could cast a world-ending fireball (a nuke), and laughed in the face of a PC raping one her entities.
And, we were just 1st level PCs - one of us trying to kill her for her loot and the other trying to find out "how the fuck is she cloning herself and switching bodies?"
Honestly, this whole "there's a problem with the game because one player wants to explore the world" is being blown out of proportion. The real issue is, as an MC you were creating barriers for the PCs (or as DST put it, MC "cock-blocking") and breaking a couple important MC principles (which you've acknowledged). You had a favorite NPC, Colt aka Elminster of AW, and didn't want to "spoil" her cool backstory or let her die so it was never revealed.
At least, that's the way I saw it as a player.
The real important part of the game that I was looking forward to,
the situations that arose from the exploration of that bunker that did arise, were drown out in cartoonish (not real) portrayal of the characters. At one point, one of the characters, Express - a driver - got inside the bunker, finally! This is what he wanted for so long, so he could kill her and take everything.
And, he had a perfect way to get her in a spot. Her "daughter" Tutu was in there. But, so was my character, Dust. I wouldn't let him use Tutu as bait, fearing collateral damage. Great. We have an awesome showcase of where our loyalties lie. Express gets pissed at Dust, but that's ok. We're still in this together.
Dust leaves to go back to his cell (it was part of his condition of being in the bunker in the first place). Express stays and waits for Colt to return in order to capture her.
Well, wizardy ensued and Express got "trapped" in the bunker in a tiny room with Colt. He knew he couldn't kill her. She would just "respawn" in an adjacent chamber and he'd be trapped there for good (put 'em in a spot for sure!). So, instead, he tells her, "I'm going to rape you mercilessly until you let me out." She sucks it up. Now, at this point, I'm emphatic because Express now has to go through the act of raping this old woman. This douchebag of a character (the player is actually cool, but his character was a douche) finally has his antics about to be spotlighted in the harshest way possible. And, to top it off, there were two characters standing on the other side of a porthole to the sealed door. They get to witness. Oh my, gripping. I'm thinking to myself, "I don't know if I can watch this" - like a scene out of Blindness.
Except, not really. Express starts raping her, she apparently loves it. Slaps him on the ass and says, "You go big boy! Gimme more!" Then, "You know what, fuck this!" Colt sets off the nuke.
And, totally deflates the whole game.
So, this whole problem of the characters wanting to "explore" the world becoming a problem isn't
really the problem. The characters exploring the world is a great way for them to interact with NPCs and that
puts them in untenable and interesting situations. How would the other characters have reacted if they had to watch the old women getting raped brutally through the porthole? Would they have said something to Express? Got retribution? Let him slide? Even with her broken fingernails on the concrete floor? Even with her blood and tears and Express' semen puddling beneath their feet when the door finally opened? That's where the game should have shined. We don't even have to watch the scene. Fade to black and cut to when the door finally opens. Express just went Aggro on an old lady by raping her to do what he wants. That's fucking serious shit. Express wanted to "beat" Colt
that bad.
Instead, we skipped that and went into this weird and unsatisfying bout of back and forth between Dust and Colt about what the fuck is going on in this bunker. Certain, he's not going to get any answers out of her, he opens his brain. It doesn't work. This bunker is immune to opening your brain. So, we finish the session with this awkward scenario sitting in a Cape Cod kitchen eating donuts and scrambled eggs. :)