Upside down diagrams In the good old days when I saw a chess diagram I didn't have to guess which way the pawns were going; there was a convention that the white pawns moved up the board. When and why did upside down diagrams become fashionable? Does it have something to do with playing chess on the internet, or did this foolishness come before the internet?
And why don't they ever rotate the diagram 90 degrees, to give us the kibitzer's view of the board?
Flipped boards are useful when the observer is supposed to control or think as if he were controlling the black pieces. That makes sense because in on-the-board games you play the perspective of white if you're white, but play the perspective of black if you're black, so in the latter case you see a flipped board. It seems pretty reasonable to me.

And why don't they ever rotate the diagram 90 degrees to give us the kibitzer's (spectator's) view of the board?

The most likely reason is that players are simply not as comfortable with that view as with ordinary 0, 180° degrees view (people play more than they watch games).