As someone who has worked as a tour director mostly in the U.S., I find this thread amusing. My passengers were Americans, Australians, South Africans, British and New Zealanders with a few from Hong Kong thrown in for good measure. And a few english speaking Germans and Scandinavians. (Surprisingly all in their 20's)
Let's focus on the Americans. Who were they? You'd be surprised. They were not all seniors. I had everything from mid-30's to mid-80s. (Non-Americans skewed lower.) Most took the tour for the same reason Americans take tours anywhere else--they wanted someone else to make all the arrangments, do all the driving, and tell them what they are seeing. We didn't just visit National Parks. Major cities were included as well. And while the history may not go back as far as Europe, the different cultures and ethnicities made for some good walking tours. (One of the most popular was a walking tour of Chinatown in San Francisco. We covered the history of the area as well as the role the Chinese played in building not just that area but America as well.)
Trying to cover the entire country in two weeks is crazy. Most Europeans didn't get the size of this country. Consider this, if you take England and Scotland--forget Wales for a moment--and then double it on top of each other so it's Scotland-England-Scotland-England--that's about the size of California. New York to Miami is similar to London to Rome (flying). London to Tel Aviv is still a couple of hundred miles shorter than New York to Los Angeles by air.
Would a Rick Steves tour work in the U.S.? It might. But it would be different. Not as much art and churches. Plenty of history but it doesn't go back as far as Europe. The hotels would be different.