In my opinion this is the effect of more millenials becoming working adults on the tail end of the recession.

1. Millenials value traveling and experiences very highly
2. Fitness and health is a priority
3. Visiting national parks and camping can be more affordable than other types of vacations.
4. Social media spreads the word

I remember going to Moab during President's Day weekend in Feb 2010 and it was a ghost town. Hotel room was cheap and nobody in the parks. There was some snow on the ground up top in Canyonlands, but not anything stopping tourists from seeing the sights or hiking.

Those days are long gone.