[Cervino]

Quite a few years ago, I live across from a chalet-style bungalow where two teenage sisters occupied the top front bedroom. They were already living there when I moved in and so they were well set in their pattern of habitation, so to speak.
Even just watching them from across the road you could tell that there was obviously terrific tension between the two of them - you'd see Sister A kicking Sister B's belongings onto her side of the bedroom, that kind of thing. On ocassion, you couldn't miss the screaming arguments between them. And once Sister A threw Sister B's make up out of the window.
The point of this post being that neither of them could be arsed to close the curtains for most of the time, and I think it was because neither would take responsibility for opening them again. Closing the curtains would also have been an act of protection for the other sister - which neither was prepared to do. And so, there the sisters were on display as they tried to out-b*tch each other.

So I think reason D in George VI's original post is "Sheer, bloody-minded b*tchiness".