Because of this game in 1982:

Although the teams were regarded as rivals (Austria beat West Germany 3–2 in a remarkable game in the previous 1978 World Cup), the game is widely seen as being fixed, with both sides having an unspoken agreement to play for a 1–0 German win. As a result, FIFA ruled that in the future both final group matches must start at the same time, so as to prevent such an event ever occurring again.

And

After 10 minutes of furious attack, West Germany succeeded in scoring through a goal by Horst Hrubesch. After the goal was scored, the teams appeared to kick the ball around aimlessly for the rest of the match. The team in possession of the ball passed between themselves in their own half until an opposition player came into the vicinity of the ball. The ball was then passed back to the goalkeeper. Isolated long balls were played into the opposition’s half, with little consequence. For the next 80 minutes there were virtually no serious attempts on goal. The only player who seemed to make any effort at livening the game up was Walter Schachner, though he had little success.

This performance was widely deplored by all observers. ARD commentator Eberhard Stanjek at one point refused to comment on the game any longer. Austrian commentator Robert Seeger bemoaned the spectacle and actually requested that the viewers should switch off their television sets.

Likewise, many spectators were not impressed and voiced their disgust with the players. Chants of “Fuera, fuera” (“Out, out”) were screamed by the appalled Spanish crowd, while angry Algerian supporters waved banknotes at the players. The match was criticized even by the German and Austrian fans who had hoped for a hot rematch of the 1978 World Cup match, in which Austria had beaten West Germany; one German fan burned the national flag in protest.

The Algerian football officials were furious and lodged an official protest. FIFA ruled that the result be allowed to stand, but they introduced a revised qualification system at subsequent World Cups in which the final two games in each group were played simultaneously.

Amusingly, some people are super annoyed by this. To me, people whining about it are just not paying attention to the rules. Sure, the rules of a soccer match are one thing, but the rules of a tournament — especially one as important as the World Cup — can produce other incentives for play not strictly speaking in line with the goals of a single match. West Germany and Austria didn’t have to overtly collude to get to this point; they just had to both realize that they could both advance with a given result, and behave accordingly. It’s absurd to insist they should have behaved any other way.

This isn’t the only example of soccer tourney weirdness, either: check out the 1994 Shell Caribbean Cup.

There was an unusual match between Barbados and Grenada.

Grenada went into the match with a superior goal difference, meaning that Barbados needed to win by two goals to progress to the finals. The trouble was caused by two things. First, unlike most group stages in football competitions, the organizers had deemed that all games must have a winner. All games drawn over 90 minutes would go to sudden death extra time. Secondly and most importantly, there was an unusual rule which stated that in the event of a game going to sudden death extra time the goal would count double, meaning that the winner would be awarded a two goal victory.

Barbados was leading 2-0 until the 83rd minute, when Grenada scored, making it 2-1. Approaching the dying moments, the Barbadians realized they had no chance of scoring past Grenada’s mass defense, so they deliberately scored an own goal to tie the game. This would send the game into extra time and give them another half hour to break down the defense. The Grenadians realized what was happening and attempted to score an own goal as well, which would put Barbados back in front by one goal and would eliminate Barbados from the competition.

However, the Barbados players started defending their opposition’s goal to prevent them from doing this, and during the game’s last five minutes, the fans were treated to the incredible sight of Grenada trying to score in either goal. Barbados also defended both ends of the pitch, and held off Grenada for the final five minutes, sending the game into extra time. In extra time, Barbados notched the game-winner, and, according to the rules, was awarded a 4-2 victory, which put them through to the next round.

Again, whining about the players’ actions is absurd. The tournament rules created the incentive, and footballers generally want to win. Q.E.D.