The industry is rife with corruption and misaligned incentives. Kick-backs are common. Bids are often not truly competitive, and when they are, people find ways like change-order abuse [1] to subvert the system. There are so many ways to rig the bidding process (bribing someone to find out competitor bids so you can undercut them) and the execution (cutting corners that you don't expect someone to find out about, or just bribing whoever is overseeing quality who might detect the corners you cut).
Even the US Army Corps of Engineers has had massive corruption cases. When I was in the industry this was an open secret, which surprising to me given the Foreign Corrupt Practices Act... eventually this would be cracked down upon [2], but as far as I've heard, still common.
[1] https://guide.iacrc.org/potential-scheme-change-order-abuse/
[2] https://www.justice.gov/usao-dc/pr/former-us-army-corps-engi...