King's Indian Defense vs Pirc Defense

What is the main difference between King's Indian and Pirc? They look very similar.

The difference is the pawn on c4. It gives White a huge space advantage in the center and favours further queenside expansion, but at the cost of falling a bit behind in development so Black's piece play on the dark squares can become a problem. Also the pawn at c4 makes the Bf1 quite bad.

The c4 push weakens d4, hence Black's early e5, attacking d4, and d4 being a dream square for a Black Knight.  Also, the c4-pawn prevents b7-b5, and hence no b4 by Black to dislodge the c3-knight.

In the Pirc, with the pawn on c2, not c4, Black does not go for d4.  White can move the knight and kick anything on d4 with c3.  Instead, with no pawn on c4, Black goes for b7-b5-b4, dislodge the Knight, and trying to win the e4-pawn.  It is especially weak if White plays f4 (Austrian Attack).

So just because Black's piece placement after 5 moves is the same means nothing.  There are 32 pieces on the board, not 16!

No difference unless U are a GM.

It White plays with early e4 and c4, there will only be transposition subleties as a difference.

But after 1.d4 Nf6 2.c4 g6 White doesn't have to push his pawn to e4 (after preparation with Nc3 etc.).

And after 1.e6 d6 2.d4 Nf6 White doesn't have to play c4 (influence in the centre), but can try c3 (taiming the Bg7) or leaving it at c2 for the moment (quick development).