>>543501632
When defense is overwhelmingly strong attacking is throwing the game, so if offense isn't stronger than defense the game doesn't get played. A "defensive" game is 2 people staring at each other, so games have to be "offensive" to conclude.
This was a thing in early magic design as well. Without strong enough encouragement to attack, players would just build up huge walls of creatures and nothing would happen because attacking would put them at a disadvantage.