Because it’s far more simple to shut down an offence than create one. Look at Switzerland vs. Spain: the Swiss closely tracked the man with the ball and even opted for a man-to-man marking in some instances to deny the more creative Spanish players even the opportunity to receive the ball without hassle.
Both can be done by physically fit players who are vigilant and/or experienced enough to not fall easily for a trick. And if you add cooperation to the individual effort (a second defender close by in dangerous positions to ensure that the attacker can’t just push the ball forward to go around the defender without meeting another one, other team mates guarding the lanes for a dangerous pass etc.), any offense will have a hard time to score.
Basically, you don’t need particularly gifted players for good defence, it can be done with reliable and hard team workers – and you’ll find these guys everywhere in abundance; but to break them open, you need talent, training and a fitting counter-strategy.
Still, no defence can prevent chances for the opposing offence completely: either the defenders make a mistake or the offence finds a way in (there is always somewhere an open space for a vertical or diagonal pass, a quick attacker or a sharp shooter) but they still need to get the ball behind the line, which means: every missed chance is another opportunity irrevocably gone by in a limited amount of time while any mistake by the defence might still result in nothing but a brillant save or an embarrasing blunder.
So, the odds are in favour of the defence but defence neither wins games nor tournaments. Inter Mailand won the Champions League this year against far more offence oriented teams like Barcelona and Bayern München/Munich. But they wouldn’t have done so without a brilliant attack, perfectly suited for quick and decisive counter strikes.
North Korea vs. Brazil has shown the limits of a defence that isn’t unburdened from time to time by a competent attack that forces the opponent to reconsider its approach aka reposition its own defence to rather safeguard the own goal instead of focusing on a supporting role for the attack.
In comparison, Switzerland was less defensive oriented while Spain was less organized in their backward movement. The result was still a fluke, if they replay the game ten times, I doubt that the Swiss would win more than twice, but it wasn’t unfair: Switzerland earned it with hard work and Spain deserved it for their mediocre play.
Still, I am a bit surprised that defensive strategy is once again so much the focus of a team’s efforts. Spain demonstrated not just the beauty of a relentless attacking game two years ago but also its effectiveness even against tactically astute and disciplined teams.
But now quick offence powers like Portugal and Côte d’Ivoire show us positionally perfect defence while playing an offence that seems cluttered and slow.
But it’s only the first round; the offence will find ways to adapt to the present defensive plans. I still expect a better attacking game in the following rounds.