[tvanantwerp]

Simple case of distributed costs and concentrated benefits. Imagine a corrupt bureaucrat who demands a small bribe from every person who needs them to perform a service. It's a pain, but the bribe is small and it's just this one bureaucrat this one time. The bureaucrat, of course, is doing this to everybody, so they amass a great sum even though every person pays a small amount. The bureaucrat can put a lot of effort into maintaining his corrupt position. But for the people who pay the bribes, it's not worth it to upend their own lives in a crusade against that one corrupt official over the matter of a small bribe.