Yeah - you gotta remember that the US is really very big, and most people live at least several hours away from the nearest ocean. Sure, there are freshwater lakes and rivers and such, but those usually aren't clear enough to snorkel in. Add in the fact that the water in the northern US oceans is too darn cold to really swim in most of the time, and you end up with only a very small proportion of the US population who live within reasonable travel distance of somewhere you even could snorkel. I suspect the number of people living in Hawaii, Florida, California, etc. (the warmer coastal states) who regularly enjoy surfing/snorkeling/other beach activities is pretty similar to what you'd find in other, similar areas in the world. Plenty of people may go to the beach as a holiday trip, but that's more to splash around or sunbathe - snorkeling isn't usually something you learn how to do if you're only there once every few years.