Chuck doesn't. Maybe he can't, on account of the wound and being tethered by Sam's soulbit or however he explained it, but Zachariah was literally a pencil-pusher angel (with admittedly exceptional additional talents) and he could manage a little pocket universe. I think we're supposed to imagine those as being more temporary and blank at the edges than God's full on worlds, like Cone World. Even Castiel took Dean bodily to the past for a while. (I mean, I guess technically, human magic has allowed for time travel at this point.)
But Chuck didn't do any of that and just Christmas Carol'd it up. And why? Because he wanted to assert Sam's helplessness in averting the situation (where Zachariah was trying to incentivize?)? Because he wanted to hear himself talk?? Because it kind of seemed like he just wanted to hear himself talk, and play the role of narrating to Sam in ways that he couldn't if he just let Sam loose to run amok. Which I suppose is what he does on a normal day, where he doesn't usually get to be Attenborough.
I guess I shouldn't critique his choice, since it ended up working out for him, but seriously, Chuck?
Also, I mentioned after the mid-season finale my sudden DEEP CONCERN that Sam's relationship with Eileen was might be intended as some key part of our finale, and how much I VERY MUCH did not want that because it would feel so counter to what I believe the show is about. But I also acknowledge that like, I'm simultaneously feeling a little "die a hero, or live long enough to see yourself become the villain" about it, as someone who has always championed characters like Jo, Bela, Ruby, Lisa, and Amelia. And why would Eileen's role be different? (BECAUSE IT'S THE SERIES FINALE, THAT'S WHY. AND THINGS GET SQUIRRELLY WHEN ENDINGS LOOM.)
Hilariously, after Sam and Eileen's (very nice--holy crap Sam, go get it) kiss, I feel nine thousand times better about the whole thing, because it felt clearer to me where Sam and Eileen might live in relation to the rest of the endgame. It probably helps that it feels a bit doomed, haha, because I think the whole notion has been fundamentally soured for Eileen, but I don't think that's the whole reason it now feels more amenable to me. It's not like I begrudge Sam happiness or relationships. It just feels like it's anchored somewhere now, and that somewhere is separate from what I perceive to be the gen core of the show.
I mean, I could always be wrong. I will say that if there's something SPN does that I find is in diametric opposition to literally anything I might want, it does tend to become a major fixture in the show, so there's that. XDD
Top Three Things That Exemplify This:
1. Me thinking while watching S4 for the first time: "My god, I hate angels talking to angels. We should do less of this." AND HERE WE ARE.
2. Me still kind of wishing the bunker would burn to the ground, after seven years of kind of wishing the bunker would burn to the ground (and relatedly, not being into Men of Letters stuff generally, and then it turning out there were more of them LOL).
3. Me disliking 11x20 more than any single episode of television, in any show, ever, and look where we are now. Chuck! Chuck everywhere!
I'VE JUST ACCEPTED THAT THIS IS THE RELATIONSHIP WE HAVE. But so it goes. My motto for S8 was "man, S8 haaaaaaaaates me, but I'll be honest, I like it all right. Show me what you got" and that's pretty much my approach to anything I don't care about that SPN then doubles down on. XDD Either that or I ignore it and/or put an art deco pool in it.
And besides, for every massive, ornate bunker underground in central Kansas, there's always a couple very excellent groady SPN bathrooms.