We walked from Burgos to Santiago in late Sept./Early October. We met a total of 4 Americans and I saw another guy carrying an American pilgrim credencial, but didn't speak with him. I think most of the reasons have been hashed out but I'll put in my two cents.
Vacation time: We had several conversations with people from the UK, Holland, Germany, Australia, etc. about vacation time Most of these places have mandatory 4 weeks off, where in the US you are not guaranteed anytime off. Also in the US, the time off that you get usually has to be used in a calendar year. Carrying over time isn't usually an option (except maybe a week) and taking unpaid leave also is not usually an option. My husband works for a rather generous company and gets 3 weeks off and can carry over a week, so he could have a total of 4 weeks off (plus holidays) every other year. He carried over a week because I had been working places with far less vacation and we took it this year. It was a pretty big deal for him to take off 2.5 weeks straight. Of the Americans that we met, two were retired, one got laid off, and one quit her job. I personally would not have had the time to even do part of the Camino, except for the fact that I had been laid off.
America is big and there is lots to see: There is plenty of stuff in the U.S. that I want to see and haven't seen yet. Doesn't always make since to travel far away to see stuff, when you haven't fully explored your own backyard.
Cost: Plane tickets to Europe usually aren't cheap. We stumbled upon the sale of a lifetime and flew for $210 round trip each ATL-JFK-Madrid (That is not a typo, it is true. I kept waiting for Delta to send me an email saying they were going to need to charge me more). Also, the exchange rate is not so good. It was $1.40 to $1.50 for 1 Euro when we were there. So technically everything is 50% more. I discovered this to be true when I needed to buy new trail shoes. I could have gotten the same shoes in the U.S. for $40 less, but I needed them then, so what could I do
Language: Most Americans can barely speak proper English, much less a second language. We don't even get the chance to start learning in school until high school. In many countries in Europe, they start learning English or other languages as early as kindergarten. I took 4 years of Spanish in school and spent a few weeks in Spain in college, and I struggled to communicate on our trip at times. A lot of people don't want to struggle on their vacation, they want to relax and not have to think or worry.
Your personal idea of fun: When we tell some people that we hiked 400 km for vacation, they sort of look at us and say "that doesn't sound very relaxing." Also, many people ask what sort of group we went with. When we tell them that we went on our own, no guided tour, they are amazed that we could figure out the logistics. And/or they are surprised that we are that adventurous to go somewhere that we don't exactly speak the language and don't have pre-booked accommodations every night.
I actually thought it sort of nice that we didn't meet many Americans. If we had, we would have just talked about American stuff. It was fun to discuss things with people who live in other cultures, and also to have conversations in broken english/broken spanish and try to understand each other. Before bed one night we had a lovely conversation with a Spaniard about what sports we liked and played. We talked about cycling and Alberto Contador/Lance Armstrong, basketball, soccer, etc. It is kind of like talking to a 3 year old when both of you only speak a little of the others language. Lots of hand motions and laughing