An article from National Parks Traveler highlights the economic value of designating parks as national parks.

The data predates the COVID pandemic, so it's unclear how things might be different now, but data showed a 55% increase in National Park visitation between 2000 and 2017 versus a 2% increase in visitations to National Monuments. Such a trend has led to a push in elevating parks currently designated National Monuments to the more prestigious National Park moniker.