The fact is that megaprojects basically never come in anywhere near their schedule or budget. That's because of a selection bias. When you crunch the numbers honestly, megaprojects come out as a terrible on a cost-benefit or ROI analysis. The ones that get built are built by people who choose to ignore the honest figures in favour of the shiny, optimistic ones. Et voila, another farce.
There are lots of other factors, but that's the core one that precedes the others.