Why is Black supposed to attack on the kingside in the King's Indian? Why does the tag wiki for King's Indian say that most of Black's attacks focus on the kingside? I have found that most of my games result in play on the queenside due to my dark-squared bishop, and sometimes I gain semi-open a- and b-files for my rooks.
There is a general principle that says that, in positions with a blocked center, every side must attack in the direction where his own pawn chain points to. For example, in the KID, sometimes White has pawns in e4 and d5 (White's pawn chain) and Black has pawns in d6 and e5 (Black's pawn chain). So we see that White's pawn chain points to the queenside, while Black's pawn chain points to the kingside.

The most efficient break move hits at the base of the opponent's pawn chain. So, for example, the base of White's pawn chain is the e4 pawn, so the most efficient break move for Black is f5 (and this is a kingside attack). The base of Black's pawn chain is the d6 pawn, so the most efficient break move for White is c5 (and this is a queenside attack).

If Black does not play e5, and he plays c5 instead, the argument above does not apply, and Black's strategy changes. Even if Black plays e5 and White decides to exchange with dxe5, opening up the center, then the situation is completely different. The KID is not a one-plan opening, it is very rich, I wish I could understand it better! 

Another example of the aforementioned principle is given by the French Defense, where sometimes White has pawns in d4 and e5, and Black has pawns in d5 and e6. In this case White attacks on the kingside, and Black attacks on the queenside.