It is definitely a size of urban area thing. In the big cities such as NYC the riders do not have access to long stretches of roads without lots of traffic or riders. So they are seeing big bundles of riders on every ride. I live in the suburbs of Richmond Va. I can go a couple of miles and be out into the rural areas away from the congestion. Even if you live in the City of Richmond proper, 4 or 5 miles in any direction gets you out of the city and congestion. Now for you big urban city dwellers imagine living where you can ride for 2-4 hours and not see another bike, rider or auto of any kind. Where there are stretches of no cell service, gasoline or convenience centers of any kind for 50-150 miles. Places where you are hoping to see cars and other riders to wave or nod to. Those places still exist in the west.

Shameless plug time. I was raised in the Wichita Falls, Texas area. If you are into century rides then you know next weekend is the annual Hotter-N-Hell 100. The one of the largest sanctioned bike ride in the country. Nothing but you, the 100+ heat and wind, the buzzards, long stretches of flat nothingness wasteland, and 13000+ other riders! Check out the link. http://www.hh100.org/