He ghosted me and the interviewer. I’d been working with him for MONTHS to help get his life straightened out.
I still have no idea why he did it.
Typical people are all, pretty much, the same. Non-typical folk are different in their own ways. There is no single path to getting someone back up on their feet. This is one reason why anti-poverty campaigns - particularly the "mutual obligation" style of welfare - fail.
The other thing that makes me wonder if it's a cultural gap is that you mentioned he was going to be able to make twice as much as he was making before for doing the same thing. If it's the same work as before, what's the difference if not cultural? Learning to talk a certain way about the things you do, use more professional language, present yourself a certain way, and ditch the people you work with if you can earn more money doing the same thing. Then he's eroding his value for loyalty by learning to bullshit the people he work with on a regular basis, because he's acting in a way that's not how he normally acts, and he's established a precedent that he's willing to ditch his new coworkers for an entirely different batch if he can make more money by doing so. He might look at that and look at the friends and/or community he already has and decide he doesn't like where that path might lead him.
That could also explain why he ghosted you. He might feel ashamed because he feels that he owes you for genuinely trying to help him. But how can he repay you except by accepting your help? And explaining where he's coming from would only lead to an ugly conflict or you convincing him that he's irrational and should just take the job -- but he's already decided he doesn't want to go that route. If he cuts all conflict, nukes it from orbit, then he can get on with his life however he wants to.
The only thing that made any sense to me was some type of loyalty to the place he was working (commercial HVAC company) but it always seemed like this place treated him badly. He’d been there for almost 3 years though with the prospect of a raise dangled in front of him like a carrot and never materializing.
If everyone in the world thought like you, the world would be a better place. Unfortunately, this world is full of nepotism and tribalism. But people like you (and the parent commenter) help balance it out.