There was a post on Reddit once where a family was tearing down their old vacation home, I guess to rebuild. And they got to the bathroom, only to discover that the entire bathroom had been built inside an old Ford Transit van, and they'd never even realized. And the bathroom was on the second floor ....
I mean, it doesnt look the prettiest, and Im not sure how good it is with regards to structural strength and insulation and such, but if you can make it work, and you have an old dead van, its not the worst way to get some use out of something that would otherwise just be junk?
It's got a whole ambiance of its' own, from the inside.
I'm pretty sure that van's table and the booths would make a pretty good spot for beer drinking. You also have ice cold beers just a couple of steps away, in an actual kitchen fridge and not a portable cooler.
Also, in that space one could keep using the car's stereo.
I would guess HOA rules (that ban things in a certain way, like no "disconnected" living spaces or nothing with different styling, limit on parked cars) or something like that.
Or maybe it was a bet or fun project for a past-its-life vehicle.