Because we use State Plane or other coordinate systems to align the work to it's actual location on the panet.
Unlike most Architectural plans, that are often tied to nothing in the real world, as is say 0,0,0.
This leads to some interesting discussions regarding each professions methods.
The Architects would be well served to base their actual site plan on the actual surveyed location.
Although some do, most wont, and that's all I'm going to say about it.