Why Can't Black Play King Takes Queen?

I understand that it's moving into check. But I thought check was a position such that your opponent could capture your king on the following move. That isn't the case here as White's bishop is pinned

No. You see, even though the bishop is pinned the move is illegal because the King is moving into check -where the king has a valid attack angle on him open by an enemy piece- if the game was to continue, Black would take the queen and White would take the king, ending the game. But it wouldn't, because it is illegal. 

It doesn't matter whether your king is taken next move, whoever's king is taken first is all that matters otherwise this would be a draw

As would this:

A game like K+Q vs. K+R would always be a draw, as would KBR vs. KR (although that one often is anyways).  It's the same thing, an absolute pin will put you in check if you move, but taking the enemy king is more important.  It's one of the basic rules of chess, the first person to lose their king loses.

The Q is protected by the g3 bishop. It doesn't matter that the bishop is pinned, the king simply cannot threaten a protected piece giving check. As a result, 1...Ka8 2.Qc8# is forced.

Think, check is a preparation to take the King. It is a rule to stop capture of king. But if the king takes the queen, the bishop takes the king. Black took the king first.

I know that the move is illegal. My question is why? How can the king be in check if it cannot be taken on the following move?

And it's nothing to do with who's king is taken first. It's to do with the fact that after king takes queen, bishop takes king is an illegal move. So, why can't king take queen?

White's bishop could take the black king before the black queen could take the white king.

Isn't it apparent that if KxQ were a legal move that black would be a tempo short as white plays BxK before black has a chance to do so himself. If it is legal for black to step it into check, why can't the reverse be true?

It absolutely matters who can take the enemy king first. In essence, the game of chess comes down to who can physically capture the opposing king first. Checkmate is nothing more than the acknowledgement that the mated king can do nothing to prevent being captured on the next ply. The state of the board after being captured is not considered when making this determination.

But the bishop is only "pinned" because moving it would be moving into check.

So, if you're going to allow black to break the rules about moving into check by taking the Queen, then you have to allow white to break the rules about moving into check by taking the black king.

IF your king is under check and you have no other moves other than illegal ones, then it is called "checkmate"!

Visualize this: "LAST KING STANDING WINS!"

Because it can. If you allow one move, you have to allow both. First king to die loses the game. Of course, in chess we don't allow the kings to actually be taken. Oftentimes you will see positions where if the game went on for just one more move or if the rules were slightly different the game would be decided in another's favour. The rules are what they are, though. 

It is illegal to place your king on a square in which it can be taken next move. While yes, the bishop is pinned to the King and cannot really move, it is still perfectly able to defend squares. If the King took the Queen on f7, then the Bishop could take the king. Making the argument that the Bishop is pinned and cannot really take the king would be like trying to claim that you can get out of check by checking your opponent. Yes, both kings are threatened, but you would lose your king first, meaning you would lose the game.

If it is OK for the king to move into check by taking the queen why do you think the white bishop should not to be free to expose its king to check by taking the black king?

Your approach, setting up some cases where a king can be in check but other cases where it cannot, requires inconsistency. I'm not sure the actual rule can claim to be more sensible but it produces a playable game and has the elegance of simplicity.

I understand the OPs logic, and of course it's been asked before.

But I always chuckle a bit because apparently the reasoning goes like this:

"Black can move into check because white cannot on his next turn move into check"

You're trying to have it both ways, so it's illogical.

:)

Because when the white bishop recaptures the black king, all the black army dies with its commander instantly including the pinning black queen

The rules would disagree. :P