Why is move 9 e5 a blunder for black?

wow nice game

because white has a full of development and full of attack @angstg

@PhOeNiX_01839 yes, white has full of attack and that is a reason I wanted to kick white's queen out from king's side. But e5 a blunder??? common!!! why is this game so complex.

Kicking white's queen is normal he can still make a beautiful attack but great job! you made a comeback @angstg

e5 and d6 is very weak, white directly can destroy blacks right to castle with lb5 and the king should go to f8, as bd7 would lose the d6 with qxd6, f.e. bxb5 qxe5+ and black is just 2 pawns down. White also will win the d6 when he plays correct in the next moves.

Chess is a complex game, as even Kramnik says.
7...e5 would have made sense, as 7...g6 8 e5 would have been strong for white.
9...e5 blocks the diagonal of your Bg7, leaves a weak backward pawn at d6 and a weak square at d5. 9...O-O would have been much stronger: protects Bg7 and Bg7 alone will drive the queen away from d4.
9...O-O is a developing move, 9...e5 is not: pawn moves are no developing moves.

Just in case it's not clear enough: The engine marks inaccuracies, mistakes and blunders based on the loss of (centi-)pawns (and also the previous standing of the position). If the game is at level state (say e.g. +0.4) and you make a move as white that makes the assessment go down to -1.5, that move is usually considered a blunder because it "loses" two pawns worth of advantage.

You don't ALWAYS understand why certain moves are considered blunders.

@tpr so complex, i dont understand the basic. so pawn moves are no developing moves too? hmmm.. i cant play right moves intuitively even.

you weaken literally everything, this is just obvious. White is perfectly placed to exploit the weakened d5 square and the weak d6 pawn.