As I touched on in another comment, social media is a disproportionate attractor of travelers for many famous locations around the world, especially for those that are "out of the way". In addition, there is an influx of global middle class with the newly found means to travel. Over a billion people in a generation.
Even in already-popular places I think there is something about “getting the photo” that gives people this kind of tunnel vision where they’ll behave in ways they might not otherwise. It has been noticeable living near and regularly walking/running across the Brooklyn Bridge and through the Front and Washington viewpoint in DUMBO, before and after the rise of Instagram. People are aggressive, selfish, and absolutely unaware of others as they try to get their version of a photo that is taken tens of thousands of times a day.
I wish people would realize that their vacation photos should include, well, them. When I travel, I'm taking pictures of my family doing things, not the things they're doing. No one needs another generic copy of just the Eiffel Tower or the Statue of Liberty.
I recall a story I once read about an elderly woman showing her family videos from her trip to the Grand Canyon decades before. You could hear her shooing her family out of the video so she could get a good view of the Grand Canyon, and afterwards she just wished she had more video of her family, not of a landmark. There are innumerable photos of most of these places, only a few of family and friends.
