Not necessarily. Plenty of dictionaries have been written as attempts at language reform rather than as exercises in just describing existing language as objectively as possible. Noah Webster for example didn't invent entirely new words, but he pushed certain spelling reforms in his dictionary that in no small part is responsible for American vs British differences such as "Color" vs "Colour". I can't think off the top of my head of a dictionary created with significant intention to promote a specific additional vocabulary, but I'd be thoroughly surprised if its never been done before.

With the recent decline of linguistic perscriptivism falling ever more out of vogue, some people seem to have adopted a hardline descriptivist view of language as only ever evolving from unplanned organic use, which is completely ahistorical. There have been many centralized top-down reforms of language, where there was an explicit survey and analysis of dialects across a region, followed by an intentional reformation of the language into a planned form seen as more standardized and consistent. As the Roman Empire dissolved in much of Western Europe, Latin began to fracture into regional isolates that were quickly becoming unintelligable to each other. The Carolingian Empire attempted several language reforms (with varying degrees of success) to create a once-again universally intelligable language. For English, the Court of Chancery played a major part in the standardization of the language, promoting certain styles vocabularies and spellings over others.