If you saw the front of my house only, you'd probably think similar things.
My living room curtains are never pulled back - because I have a tropical fishtank in the window which does not like extra light. Due to the layout of the room its the only place this tank fits. Whilst I have a background on the tank, the window gets full sun all day and overheats the tank if the curtain is open.
The curtain in my front bedroom is also drawn, its a junk room, its too full to open the curtains at the minute.
The curtains at the back are open once the full sun is off the back of the house, I sit by them and work by them, in full sun the glare off my monitor is too much, or upstairs its casting a shadow over my drawing board.
I don't invite strangers in often, only those I need to. It requires organisation as I have a dog who would bite visiting strangers (hes easily managed outdoors but in the narrow confines of my terrace, a stranger coming in is a major trigger).
So.. good reasons that don't make me a total weirdo for not always opening all the curtains and not inviting the world and his wife into my home.
You know what though, if I liked the dark and lived like Mr Trebus, it wouldn't be any of your business!