Americans don’t do it voluntarily, but mainly because they don’t understand the way the US system works. Part of that is the nation’s legal system; part of it isn’t, but is instead international.
Regardless of whether or not today’s United States is a democracy, our legal system possesses two features that make corruption especially difficult to prosecute to conviction, and this difficulty is extreme and makes such convictions extremely rare at the top, amongst members of Congress, and Presidents, and former federal officials, and billionaires, so that people at that level need to be extremely stupid in order to be convictable for whatever corruption they might do. (And such extreme stupidity is virtually non-existent amongst that elite, most powerful, group. So, they get away with it. There is absolutely nothing to stop them.) Consequently, corruption is rampant at the top in America.
Both of these two domestic, US, features apply also to some lesser extent in every other country; and, at the end, I’ll describe the exacerbating factor that makes the situation especially bad in the United States — the international factor, which intensifies America’s corruption-problem.
Reason Number One why Americans favor corruption is that (especially at the top) corruption is, to a large extent — and very unlike lower-class crimes of direct violence — a judgment-call, largely political, and therefore specifically a partisan matter to judge. Anything that’s “partisan” is especially difficult to produce a unanimous verdict, which is what would be required for a conviction. Consequently, an individual of high status within the elite will be granted by his group or “party” every benefit of every possible doubt. This is likely to protect any elite person from being convicted.