Bingo great post @Davy Gspot on.100% right! I believe there are two main reasons :
1/ Lack of pride and integrity. Whatever work I've done in the past I always aimed to walk away having left the job as good as I reasonably could for the client and as tidy and ready for the next man as sensibly possible. Utility (road work) would be left tidy and safe. Lorries when I was in that line of work would have had lights, tyres and fluids checked and fuel tank topped up. I'd imagine most of us here are the same.
2/ Because they are let get away with it. The attitude I quite often came across in my other jobs was "It's near enough. We'll be long gone by the time that's spotted."
Do it once, do it neat, do it quickly if you're able... But above all do it right, if you can. It won't always go right. That's life. It's how we deal with problems that matters.