Sometimes politics over rules sensible debate. I left a company in the defence industry when the technical director and sales chief decided not to accept my estimate of how many man years of work would be needed to design a new tank sight. I was Chief Designer and had been hired in to buck up their design department. I had already won the contract for the image intensified night sight for the SA80 rifle for them and introduced new more efficient working practices in the design area. They over ruled me and went ahead using a lower figure which I knew could not be achieved in order to undercut our oppositon. Money was lost, the parent company sold the outfit to the French (not long after I left) and all the culprits lost their jobs.
Earlier in my career I worked for a very large blue chip company in the heavy electrical business. They had a whole department whose job it was to work how long they could delay paying their sub contractors before legal action was on the cards.
Sounds like Carillion had both these things going on.