Theory: (sum spoilers)
All Happens in Dave's head while he is in a mental hospital because he already passed thru the tragedy and got traumatized for life
He can't live without thinking what he could had done and that explain why if he choose Oz offer and leave his friends behind, then everything dissapears because that it'd be the most unreasonable thing from him to do
Also, The vault represents his sub-concious and inhabilitie to...
You know what? This is a dumb theory :"v yeetus deelectus
**SPOILERS**
Honestly this thought had passed through my head once...especially when the rat got involved. My memory might be a little hazy, but I think that at one point in a bad ending, the wording just switched to past tense like he was reliving a flashback of that timeline. And the way the background is always grayscale unless something memorable comes up like a CG kinda goes with that theme. Since the vault works on trauma, I’d figured that was the reason they’re so important and cryptic [at times]...those words are sorta like triggers, hence the sound that plays (quite a stretch, but hey). I might be heavily overthinking this, but the fact that I’m able to overthink it shows how much detail goes into everything this game has to offer.🐊
