Problem: Botvinnik vs Panov game

I bought a book named "50 strategical ideas" by Anatoly Terekhin. He details some moves of a game between Botvinnik and Panov.

On this board, the goal of the white player is to put his knight on d5. But even so, why not 1. f5 instead of fxg5 (to block his opponent game) ?

Generally a player with two bishops wants to open up the position so the bishops will have greater power, while a player with two knights prefers to keep the position closed. e4-e5 increases the scope of the g2 bishop, and takes away the e5 square from Black's knight on d7, which might otherwise occupy that square. If you look at the rest of the game, after some trades Botvinnik will have rook and two bishops against two rooks, and White's bishops are dominant; they support the advancing e-pawn, which Black's rooks are unable to stop.