Corruption in the sports sector is linked to the political system where the entire government, from election to governance, is corrupt. This has affected the sports activities in most countries and even the premier league.
FIFA and other sport governing bodies are not left out in the corruption.
Could be the case but most of the time it is an isolated case. Now that I think of it, you are probably right, if the political system is corrupt then that means that they are tolerating corruption in other aspects too.
It's only an isolated case because only a few have participated and it's hard to detect corruption in sports. But, in reality, even one person would rig a game, he can make millions of money depending on how valuable he is on a team, a star player gets more minutes so he can help in rigging the game for his favor, whether he lose or win in a particular game, what matters is he serves the purpose to win the bets on the sportsbook.