Something so sinister about the Bunker actually. It's not allowed to change. It doesn't accumulate garbage or stains or dust or damage, it's strange and sterile. There are no visible permanent additions, no hanging coats or shoes by the door. No evidence of cases. No pictures. It looks like a set, like no one even lives there. It was locked up for 60-70 years and if at any point the Winchesters packed up and left it would look almost exactly the same
The warding sigils are invisible or burned off or both. It's supposed to be impossible to get into and find, but it happens multiple times. The layout makes no sense and keeps changing. There's a garage. They lampshade in the ep Last Holiday that much of the setting is just props and largely irrelevant.
They don't let Kevin stay, they leave him on a boat somewhere (which is an idiot plot to allow him to get kidnapped by Crowley but does give us a no bunker setting that has at least SOME personality) and when they do move him in, he's still basically not there until he dies. Mary doesn't stay. Cas doesn't stay. No one gets permanent rooms. Even when the AW hunters were there, they just seemed to be borrowing the space, not adding anything to the general look of the bunker, not leaving around personal affects, trash, dishes, not having rooms. It makes it incredibly hard to care about their absence when (other than them not having personalities or names) after they all die the bunker doesn't really feel emptier. It's the same amount of empty. Same goes for when THE ENTIRE WORLD GETS RAPTURED. Everyone else is gone but because we're in the bunker, nothing looks different. You wouldn't even be able to tell
Especially when the earlier seasons sets had so much character. They were in diners and libraries and streets surrounded by people. They sprawled out in motel rooms and abandoned houses, leaving clothes and trash everywhere. Things got old and worn and dirty. Bobby's house looked like a house. The Roadhouse looked like it had people going through it. They had no home but they had the world yknow?