Chess Opening Theory/1. e4/1...e6/2. d4/2...d5/3. Nc3/3...Bb4/4. e5/4...c5/5. a3/5...Bxc3/6. bxc3/6...Ne7/7. Qg4/7...O-O/8. Nf3

=French Defence, Winawer Variation= With 8.Nf3 White develops an additional piece which can support White's efforts of attacking the Black King. However, there is still no immediate threat for Black, so there's no reason for Black to play desperate measures like weakening their pawn structure on the kingside or something like that. Hence they usually decide to develop more pieces by playing 8....Nbc6.

Theory table
'''1. e4 e6 2. d4 d5 3. Nc3 Bb4 4. e5 c5 5. a3 Bxc3+ 6. bxc3 Ne7 7. Qg4 O-O 8. Nf3'''