My preference is they not add airports that don’t exist irl. However, most of the parks in the sim have an airport within 10-20 miles of some part of the park boundary. Grand Teton is fairly unique in that there is a commercial airport within the park boundaries, at Jackson Hole (KJAC), only a few miles from the barn. This airport was upgraded significantly for this WU, but I’m not aware of any other airports that were.
However, other POIs (similar to the barn) within the parks are often dozens of miles from an airport. Some of the parks are thousands of square miles, so understandably these places can get quite remote.
Otherwise, to land close to most of these POIs or other remote locations in the sim, you’ll need to use a helicopter or another VTOL aircraft, or chance it with a conventional aircraft, maybe selecting one with large tires and STOL capability. The good news is it’s just a sim and while landing off-airport can be rough, there are no real consequences for doing so. There are also ground vehicles for purchase in the marketplace.
As an alternative, if you are on PC, I highly recommended MamuDesign’s FSExplore. With the paid version, you can get out of your plane and choose from multiple vehicles to drive from the airport to these locations in avatar mode. Or you can go to a trailhead and take a guided hike. And it’s very easy to create POIs and the trails themselves. I’ve been creating dozens of the more popular trails within (and also outside of) the national parks.