Hypermodern setting, U could read the famous book "My System" by Nimzo himself.
I don't understand the King's Indian Defense
After 1.d4 Nf6 2.c4 g6 3.e4 black allows white to put three pawns in the center, but why?? The Nimzo-Indian and The Queen's Indian Defense seem way better so I want to understand the ideas of the King's Indian and why many players like it.
First of all black can play 3.Nxe4 in the line you gave, but if white plays Nc3 then e4 we get to that kind of position. The idea is just to get your king to safety first, and then challenge the center later, most commonly with e5, but also with c5 sometimes. It's a quite advanced opening though, so i wouldn't suggest playing it at your level

After 1.d4 Nf6 2.c4 g6 3.e4 black allows white to put three pawns in the center, but why?? The Nimzo-Indian and The Queen's Indian Defense seem way better so I want to understand the ideas of the King's Indian and why many players like it.
First of all black can play 3.Nxe4 in the line you gave, but if white plays Nc3 then e4 we get to that kind of position. The idea is just to get your king to safety first, and then challenge the center later, most commonly with e5, but also with c5 sometimes. It's a quite advanced opening though, so i wouldn't suggest playing it at your level
Sorry I wrote the wrong line in my post. I meant after 1.d4 Nf6 2.c4 g6 3.Nc3 Bd7 4.e4, white's knight guards the e4 pawn so you can't take it andd white has a strong center with 3 pawns

Very short summary: black locks the center with an e5 push and takes over the dark squares, then proceeds to go ham on whites king.

After 1.d4 Nf6 2.c4 g6 3.e4 black allows white to put three pawns in the center, but why?? The Nimzo-Indian and The Queen's Indian Defense seem way better so I want to understand the ideas of the King's Indian and why many players like it.
Why? Fischer played it regularly and score well. Kasparov played it regularly with good success. The two former World Champions have millions of fans. It's normal chess fans follow the openings of their idols

If you cannot undesratnd it, don't worry.
It took me more than 4 years to understand it thoroughly, and even after all that years I rarely employ it, due to the huge amount of maintenance work that has to be done to avoid getting slaughtered at high level games.
Wow, what a relief for us, simple players! 😜 We are not obliged to understand KID!
The reason why Bronstein, Tal, Fischer, Kasparov, Radjabov, Nakamura played the King's Indian Defence is to play for a win with black. The center gets locked. White has more space and white gets an initiative on the queen's side, but black gets an attack against the white king.

KID are favorite of chess hustlers in blitz games. If White plays slow in Queenside attack, Black will advance kingside pawns.
The whole idea is to pray that White doesn't know how to convert a space advantage with chaos all over the board.

at its core, it cedes the center and a space advantage to white in hopes of creating a devastating attack by locking the center and transferring everything over to the kingside and using the pawns like a battering ram. i think. then again, there are so many different variations in the Kings indian that it makes my head hurt. which is why I play the Grunfeld as black

Did you think the grunfeld had any less theory? Nope.:.
no but I find the theory in the Grunfeld easier to understand. KID theory is insane and I cant grasp it
Did you think the grunfeld had any less theory? Nope.:.
Yes it has. Don't get me wrong, it has a lot of theory, but not as much as the KID. The Gruendeld has a lot of long lines, but it doesn't have nearly as many lines as the KID. You literally need to know what to do against everything, and i don't think it's as important to know theory in the Gruenfeld as it is in a lot of lines of the KID

Black can trim a lot the required amount of the theory he needs to learn in the KID. Here's one example:
This line is very reliable, and white has been unable to demonstrate an advantage.
In the Grunfeld, such "shortcuts" are rare.
Can't white just push d5, and then you're in an entirely different line with lots of differentiating ideas? Because i feel like when you play the KID white can choose from tons of different options and they're all unique
Black can trim a lot the required amount of the theory he needs to learn in the KID. Here's one example:
This line is very reliable, and white has been unable to demonstrate an advantage.
In the Grunfeld, such "shortcuts" are rare.
Can't white just push d5, and then you're in an entirely different line with lots of differentiating ideas? Because i feel like when you play the KID white can choose from tons of different options and they're all unique
That's what i said above. Basically everything white can play requires at least some theoretical knowledge for black, while in the Gruenfeld, you could probably play it without knowing too much theory
Black can trim a lot the required amount of the theory he needs to learn in the KID. Here's one example:
This line is very reliable, and white has been unable to demonstrate an advantage.
In the Grunfeld, such "shortcuts" are rare.
That line is still just worse according to the computer, which i suppose the King's Indian always is, but that line is bad in practice too, especially if you want to win. Look at a database and look at the scoring percentages. It's also very difficult to play with the black pieces, so i would argue you that you should play Nc6 or Na6 there
After 1.d4 Nf6 2.c4 g6 3.Nc3 Bd7 4.e4 black allows white to put three pawns in the center, but why?? The Nimzo-Indian and The Queen's Indian Defense seem way better so I want to understand the ideas of the King's Indian and why many players like it.