
It's such a stupid pearl clutching, alarmist tangent. it's impossible to budget for a household – phone dies, bills go up, Christmas is coming around – so with as many moving parts as a highway, hospital, or stadium, what do you think is going to happen? a material becomes scarce, workers strike, new legislation or standards inevitably change over four years, a political party might even turn over.
You are missing the main one, the construction companies deliberately underquote to get the contract. The government probably knows this and goes along with it anyway because it's more palatable to the public.