It's a bit simplistic to blame only labour costs. Large, complex civil projects often have cost and schedule overruns because contractors know they're going to

It's a bit simplistic to blame only labour costs. Large, complex civil projects often have cost and schedule overruns because contractors know they're going to get paid anyway so are incentivised to make the project slower and more expensive. Smaller, simpler projects don't tend to have the same issues because contractors know they can be replaced easily if they fail.