Assume, only for the purposes of argument, that 10% of all humans would betray trust for personal gain.

In a close-knit, tribal society, limited by the human brain capacity for maintaining personal relationships, where everyone knows everybody else, it is not very profitable to betray a trust. After the first time someone does it, many of their peers revoke their trust, and that person then has to re-earn enough of it to reneg again. Each time, it becomes harder to get ahead.

In order to grow societies of larger sizes, we instituted trust-by-default relationships, just to make goods move from the loading docks. If human nature is 90% trustworthy, this is 90% safe. The remaining 10% can be dealt with via retaliatory mechanisms: bond revocation, lawsuits, arrests, etc. As long as the individual responsible can be identified, and punished, there is significant disincentive to reneg.

To grow larger still, we instituted pseudo-anonymous legal fictions. We started doing business with companies, instead of people. This provided an opening for the renegade 10%. They could let the company establish trust, take control of it or a portion of it, betray the trust for personal gain, and let the corporate shell take the brunt of retaliation--if anyone ever even found out about the betrayal. The type of person who would become corrupt is drawn to positions that are corruptible: the bosses of businesses and bureaucracies, and the cronies and collaborators of those corrupt bosses. The ultimate goal of a corrupt person is to be the fox in charge of a henhouse--nay, in charge of a whole poultry farm.

Whenever we rely on structure rather than people to manage societal complexity, the structures may be attacked whenever no one else is looking. The corporation cannot refuse to do as the CEO demands, as it has no will of its own. You can't watch everyone all the time; we just can't afford the costs of that kind of labor, that only humans can do. And whatever human oversight mechanism you may institute can then be infiltrated by the corrupt 10%, who can collude to profit from failure in oversight.

Qui custodiet custodes? It's corrupt cop-watching cops, all the way down.

It's like an auto-immune disorder. How can your body possibly defend itself from its own immune system, at the same time as all the foreign pathogens? So the corruption becomes endemic, because there are not enough people watching to keep everybody honest all the time.

If you put out a tray of goods with a price label and honor box, 90% of people will pay the correct amount if they take something. It only takes one renegade to empty the tray, break open the honor box, and ruin the whole thing for everyone. Or even just to take goods from the tray without paying, one at a time, until the profits are all gone. It's not worth paying someone to watch one tray. So set up a camera to watch it. That just adds a separate camera-disabling step for the renegade. Put up a camera-watching camera. The renegade tapes a photo of the tray-watching camera over the lens, disables it, then loots the tray. It's an arms race. The only way to win is to put another human in the loop, and the instant you do that, you have to pay them, and then your profit margin is shot. Besides that, there's always the 10% possibility that the person you pay to watch your tray is a corruptible individual, and they'll just go halfsies with the tray-looter.