>This excuse only works if who built the bridge isn't central to the discussion.

It isn't central to the discussion. The appearance of corruption is clear; nailing down the culprit is difficult. It isn't reasonable to expect people to have a theory of corruption in order to complain about it.

>Otherwise this is just generic conspiratorial thinking

The perception of corruption is not a conspiracy theory. Corruption is an ordinary financially motivated crime, while conspiracy theories usually involve some kind of grandiose or mystical objective ("new world order").

Anyway, the question is moot because the only possible answer is "the regulatory authorities". We know who makes the rules! I just didn't want to tolerate this kind of fallacious nitpicking.