Although there is evidence of world cup games being fixed many years ago, we don't believe it is fair to say that the games are clearly fixed, especially in the most recent world cup tournaments. Remember, FIFA wants to sell out stadiums and make money.
One thing that goes against that is the fact that we saw several of soccer's biggest powerhouses eliminated early from the 2018 World Cup. Germany for instance who was the defending World Cup champion got eliminated in the group stage this year. Germany draws a lot of fans and attention because they are one of the world's best teams and it should be noted that their fans rank towards the top of World Cup attendance.
We also saw the World's two best players Lionel Messi and Cristiano Ronaldo make early exits from this year's World cup. These two players get significantly more national attention globally than any other soccer players.
Many popular or high profile teams such as Italy, Netherlands, The United States, and Chile didn't even qualify for the World Cup this Year. Another significant point to make is that in the 2014 World Cup referee Humberto Clavijo got replaced for making poor calls in a game between Mexico and Cameroon.
If it was so easy for FIFA to fix games and their only motive was to make money, then I don't think so many popular soccer giants would have exited the tournament early or that referees would get booted for making mistakes.