In view of the threat 4 Bh3, Black had to weaken the light squares.

Sending more pieces to the kingside, where Black can't defend himself easily due to the lack of space.

This intermediate move leaves Black unable to defend both flanks. There followed:

with the decisive threat of 19 Rg7+.

Initiating a typical minority attack.

3.a3 b4 4.axb4 axb4 5.Qd1 was a lesser evil, getting rid of the potentially weak a-pawn.

An ugly place for the knight.

5.cxb4 Bxb4 6.Bxf6 gxf6 7.h5 offered more resistance.

Now White is doomed on the queenside.