Roosevelt's terms in office saw the creation of five new national parks, but with such a small number of parks as were currently in existence (10) the system of military and scattered management that was in place during the time period worked just fine.

The Organic Act of 1916 (which Wilson signed, but never really championed per say), was overshadowed by the looming Great War that the US was soon to be involved in. And in fact, part of the rational to give the parks their own agency was that until that point, many parks (chief among them Yellowstone) were managed by the War Department and staffed by the army, which was soon to need all the active duty soldiers they could pull from such stations.

In fact, the impetus for the creation of a National Park Service came from then Secretary of the Interior Franklin Lane, who challenged a young industrialist by the name of Stephan Mather to start lobbying for such legislation.

Roosevelt commonly gets the screen time when it comes to the NPS system because he was such fervent supporter of setting aside lands for conservation, public enjoyment, and preservation. On top of five new national parks, during his terms of office the Antiquities Act of 1906 was passed, allowing presidents to establish monuments, of which he created several. His bigger claim to fame probably is the creation of the United States Forest Service during his terms in the face of fierce proposal from businessmen of that time.

Sources and Recommended Readings:

Foresta, Ronald A. America's national parks and their keepers. Routledge, 2013.

The Birth of the National Park Service, The Founding Years, 1913-33; Horace M. Albright as told to Robert Cahn; Howe Brothers; Chicago, Illinois, 1985;

National Park Service Organic Act of 1916