A national park cannot be created by the President alone, it requires an Act of Congress signed by the President. That is why very few have been added since our only two genuinely pro-environmental presidents, Johnson and Nixon. Each designation (Wilderness Area, Wilderness Study Area, National Forest, National Monument, National Historic Place, and so on) has its own statutory and regulatory restrictions and rules. For example, hunting is allowed in Wilderness Areas but not a national park. Pro-development or extraction (logging) have blocked new national parks because they know very well that once made into a national park an area will never lose that designation, which would require Congress to pass a new law repealing the original designation. The public won't go for that.
Conservationists here in Montana have been working for years to expand some Wilderness Areas and designate new ones, and see the Pinnacles designation as a great first step.