So...aside from the supervolcano why are more and more people visiting Yellowstone now?
Dear Repeat Offender,
As of 2015, Yellowstone National park had 4,097,710 visitors, and there seems to be a steady overall increase from decade to decade. There are many reasons why this is happening, but most of which I can come up with are speculative. It could be that because the population is constantly increasing, there are just more people to visit the park. Yellowstone National Park has been more and more popular abroad because of nature documentaries that feature the park, and so a lot of foreign tourists could be coming to enjoy it too. Also it could be that this year is the 100th anniversary of the National Park Service and Yellowstone happens to be popular anyway so they visit the one they know in order to celebrate. If you'd like to peruse more national park stats and come up with your own theory, they can be viewed here.