Why do these sentences all start with WHEREAS?

I am looking at the Democratic and Republican Party Platform documents, and noticed this strange wording:

WHEREAS, All platforms are snapshots of the historical contexts in which they are born, and parties abide by their policy priorities, rather than their political rhetoric;

To me it doesn't make any sense how this is structured. Why is it done this way? It seems like a bunch of partial run-on and incomplete sentences.

The clauses end with semicolons; they are not structured as complete sentences but as introductory clauses in legalese.

In the law the term whereas also is used as the introductory word to a recital in a formal document. A recital contains words of introduction to a contract, statute, proclamation, or other writing. In a contract a whereas clause is an introductory statement that means "considering that" or "that being the case."

So basically they are introducing various reasons to actually resolve the four resolutions presented at the end of the sentence. (And yes, that document is ONE sentence.)