That's not a fact. That's just an opinion.

You could just as easily claim, and still be just as opinionated, that a system is what is intended to be (intentional design theory), or that a system should be what it ought to be (normative systems theory), or that a system should evolve to fit the purposes of it's environment (structural functionism), or that there is no fixed purpose and that purpose is instead decided by social consensus (social constructivism).

A motivated reader might notice that the above systems thinking models each align with various schools of thought/philosophical schools. Idealism, telologism, constructivism, etc. This highlights the assertion that there might not be any one correct system of thought given one's stance on Truth, in that certain said systems might believe that they are the One Truth but could not logically demonstrate to the others that they are as such.

I think the closest thing we'd get to purpose for a government is likely defined by the constitution? we're not really even upholding those values