Nothing, in and of itself:). It's just that if I want to keep the wife happy (and I do), then bunker-style is out, brother.
On top of that, I wouldn't call a bunker particularly livable! But I DO love the idea of a Skyfall-style escape tunnel.
In fact, if you look closely at the hallway next...
The kitchen and the bath are the only rooms in the house that don't get direct sunlight (I don't really count the workshop/storage/laundry area). The primary living areas (living room and bedroom) both have HUGE windows that let direct sunlight practically pour in.
But your larger point is well...