Anything as big as FIFA is corrupt. The bigger it is, the more chance their is that the corruption becomes public knowledge due to the law of large numbers.
The IOC is corrupt. The NFL is corrupt. The MLB is corrupt. The NHL is corrupt. The bigger they all are, the more chance there is that you hear about the corruption. Some leagues, like the NHL, do a better job of covering one another's asses and keeping things hush hush than others, but people make mistakes, no matter who they are or what they do. To think that a monstrously huge company or organization should NOT be prone to the failings of humans simply because of their visibility is naivety at it's best.
I don't believe that power corrupts people, but I do believe that people corrupt power because they can't resist their passions and the temptation for quick and easy gain becomes irresistible. If you found $1 million in the street, would you return it to it's rightful owner?
Even if YOU would, would the person you turned it in to do the right thing? Would EVERYONE here do the right thing?
The psychology is simple: I might do the right thing, but the guy next to me won't, and since HE won't do the right thing, then I won't do the right thing and then, it stops being "The right thing" it becomes "What everyone is doing".
But, enough metaphysics and psychology for one day.
FIFA is corrupt because it hires people, and people are, en masse, piles of dog shit. No amount of scrubbing will ever remove all the stench of a pile of shit that large. Again, the law of large numbers.