Casual fans - that is people who don't really care about the strategy of football - think defensive battles are boring. And it is boring if it's between two bad teams. But a low scoring affair between two great teams can be amazing. I think of the battles between great defensive teams of the 80s and 90s like the Eagles, Bears, Giants. Epic. Every play became crucial, one big run might become the difference in the game. Try airing it out deep and the QB is probably going to end up in traction. And you could tell the players cared, they were emotionally invested.
For me it's like watching a no-hitter (or even more specially, a perfect game) in baseball. At first you are like "1-0, ho hum". Then around five innings in your begin to realize what's happening even though tradition forbids you from saying it out loud. Suddenly every single pitch is the most exciting thing in the world. One bad pitch would end it but if he can keep it up .... history!