Why is this a bad pawn move for black?

Can someone explain to me why Stockfish (and other engines) think this is a bad move for black 4 ... e5:

1.e4 c5 2.d4 cxd4 3.c3 dxc3 4.Nxc3 e5

It shifts the advantage from -0.3 to +0.3. Surely black can defend the pawn and reinforce with Nc6 and d6 or Bd6? I am not a high level player so pardon my ignorance.

Here is the board position:

Eeasy.it weakends d5.i play myself morra and sicilian.you should play after Nc3 e6 Or nc6

Yes 4...e6 or 4...Nc6 or 4...d6 are all good. After 4...e5 you nullify the advantage of your extra pawn. How will the extra d-pawn ever promote to a queen? You turned a healthy d-pawn into a backward, weak pawn.

Thanks for that answer. But why is d5 more important than say attacking d4? I thought all four center squares are equally important? Is it because of the harassment that can come from white Bc4 and threatening Qf3 or Qh5?

Thanks tpr - that also makes sense.

@pwnell #1
Many years ago almost all chess players thought that e5 in Sicilian defense was plain bad. It weakens the d5, d6 (and f5) squares, and usually black ends up with a backward d6 pawn as well.
However, GM Sveshnikov and others have shown that the e5 move in Sicilian defense is viable.
In fact, in some lines of Sicilian Najdorf e5 is a standard reply.
And in some lines of the Smith-Morra gambit, black works towards pushing e5.
In the position that you asked for, ... however, you are giving white time for developing pieces in exchange for a pawn. The bishop on f1 can nicely go to c4 since you also cannot block the a2-f7 diagonal easily (Which is possible with e7e6, when not having played the e pawn to e5).
Comparing the position of yours with Sveshnikov and Najdorf positions, you will likely find that in those other positions black was more ahead in development.
So, your suggestion e7e5 is not a mistake, but you have better moves in that very position.

I searched for some more on Svesnikov to read,
here's something :
www.chess.com/article/view/sicilian-sveshnikov3

HTH

Thanks this is very insightful.

@achja In the Sveshnikov, Najdorf... there is a white pawn on c2. Here it is missing, so the d-pawn is here a candidate for promotion. If black can fend off the white attack, then black wins the endgame with his d-pawn.

In Morra it is usually played later even with a loss of a tempo e6-e5. Chess is very concrete, there are no „golden rules“. It is mainly designed to prevent an e4-e5 by white. It you pre-prevent it too early white plays differently though

There are lots of games, e.g.