missing theory in openings

| 7 | Opening Theory

there is something strange about opening theory , maybe its due to lack of my knowledge (which is most probably the case) but at least its not found in many books about the subject..... now let me share my question with   you in a usual queens pawn opening and black intention of kings indian reply 1 d4 Nf6 the main line goes with 2 c4 which is the usual reply by white according to most books to allow 3 Nc3 without blocking the c-pawn , then the main line continue as follows 1d4 Nf6    2c4 g6    3Nc3 Bg7    4e4  d6    5Nf3 o-o        now white aims r very clear to make a wide centre (sometimes he plays 5 f4  to make 4 pawns attack) very fine and look at the first moves in the pirc defense  1. e4 d6 2. d4 Nf6 3. Nc3 g6 4. f4 Bg7 5. Nf3 O-O   which is considered by far the majority of first moves in pirc as u notice black makes the typical first moves except that d6 preceeds Nf6 (which is clear bec in pirc its a kings pawn) the question why on earth u dont find in the literature the usual white reply of c4 based on the same idea that he is willing to make wide centre and makes c4 before Nc3 so as not to block the pawn ? its very rare to find this move in pirc ....what is the difference? black actually makes the same basic moves exactly , why dont we find that as major variation at least in pirc ? is it something psychological that players who will to play king pawn dont want a semi closed opening that KID creates?