It can't advance without being captured. en.wikipedia.org

This endgame is a very interesting one. While black retains the bishop pair, he cannot properly utilize it to it's full potential due to the semi-closed nature of the board. There are still too many pawns interfering with the bishop paths, and only one bishop is able to capitalize. The other side has a bishop and a knight, and one fewer pawn, but black's extra pawn seems to be able to restrict the knight's movement heavily and influence it's capabilities heavily. It's quite a scenario and highly reflective of many of the positional aspects I face on my level OTB.

True, but from d8 the bishop would attack b6.

Without the bishop pair, the drawing chances increase significantly.

e3 and then c4 - as in the game.