After 1.d4, why doesn't White play 2.e4 when he has the opportunity to do so?

After 1.e4, when White has the opportunity to play 2.d4, the best move according to the engine is 2.d4, and White plays 2.d4 about 90% of the time.

After 1.d4, when White has the opportunity to play 2.e4 (meaning when Black plays for example 1...e6, 1...d6, 1...g6, any move other than 1...c5, 1...d5, 1...e5, 1...f5, 1...Nf6), the best move according to the engine is 2.e4, but White plays 2.e4 only about 23% of the time.

Both when White plays 1.e4 and when White plays 1.d4, White often gets a Pawn on e4 and a Pawn on d4 and a Knight on c3. But the difference seems to be that when White plays 1.d4 White also has a Pawn on c4, while when White plays 1.e4 his c-Pawn remains on c2 blocked by his c3 Knight. When White plays 1.d4, he will play c4 first and only then e4, he will not play e4 before playing c4.

Most players who play 1.d4 are trying to get away from 1.e4 lines.

So they often favor d4 + c4 vs. any other move to keep it the lines more in the Queen Pawn lines.

1. d4 e6 2. e4 d5 is a French, not part of the 1. d4 player repertoire usually.

1. d4 d6 2. e4 Nf6 is a Pirc, something you're not supposed to meet as a 1. d4 player. What to do instead is an interesting problem : 2. c4 e5, 2. Nf3 Bg4!?, and against 2. g3!? Black can simply go for a King's Indian.

Against 1... g6 if you don't play a quick c4, you will find yourself against a Tiger Modern, something you usually don't have any clue about.

I would say it's because 1.d4 players want a more quiet positional game, but playing both d4 and e4 early in the game would lead to more sharp play. If those players would want a sharper game they'd play 1. e4.

When Black allows 2.e4, I view it as Black "asking" for a transposition into an e4 opening. That suggests that's he's looking to play his favorite 1.e4 defense.

As White, I believe the best strategy is to try to deny Black from getting what he wants, if possible ...

Plus, 2.e4 might be the engine's top choice, but it's not much better than 2.c4 overall. They both fizzle out to a draw with best play, regardless. Just two different paths up the same mountain.

The trick is to choose the path that you think you can make more treacherous, for your opponent to go wrong ... For most d4 players, I believe they'll choose the d4+c4 path for that.

1. Black plays second, not white.

2. There are many types of openings.

3. I doubt that you are an actual North Korean

I would like to change that.

3. I doubt you can identify flags