For the same reason they never go on time. Because for them to do so, every single thing needs to happen perfectly, while to be late of over budget, a single t

For the same reason they never go on time. Because for them to do so, every single thing needs to happen perfectly, while to be late of over budget, a single thing needs to go wrong. Over budgetting doesn't work because then your customers won't chose you when the bidding starts.