I've always been fascinated by this question and have often tried to find a single, simple motivating factor that would give complete satisfaction to my inquiries. However, I've come to a growing realization that like my own life choices and those of everyone I know -- there is usually a great multitude of motivators that impact any given decision but especially those decisions about residence and work. To visit Gordevio and the surrounding area today, the question is even more puzzling: Why would anyone ever want to leave such majestic beauty, such apparent economic vibrance (one of the highest standards of living and weathiest countries in the world), such invitingly warm mediterranean climate, all in a country respected for its peaceful neutrality? But life wasn't the same in the 1800's. It didn't matter how beautiful the country was when there was widespread famine.
As previously noted, my "Nana's" family emigrated directly to the USA -- but my grandfather's family emigrated from Someo to Australia and then to California. One web site reports that the first two Ticino migrants to Australia arrived in 1851 and paid their own way. Two more left in 1852 and "it was perhaps the successful return of two of them in 1854 which caused the general exodus of 1855 when 1073 arrived in Australia...[T]he Ticinesi who migrated to Australia were, mostly, from the ... the villages in dead-end valleys."
(See: http://www.eye.ch/swissgen/kant/tiemau-e.htm )
Another web site gives some interesting perspective to emigration from Switzerland (of course, like most web sites -- it's impossible to determine the accuracy): http://jeanmarc.vonallmen.club.fr/emigration/index.html .
Why do the Swiss-rooted family trees spread to Holland, Australia, Illinois, California? Was the Catholic church involved in either making funds available, encouraging or directing such emigration as has been suggested? Were ancestors motivated by the lack of food -- or was the desire for adventure, perhaps riches, even homesteading among the motivators? It's fun to continue to research the question and to ask for the opinions and knowledge of all family members -- but I fully expect that there is no easy, single answer. Indeed, I can only wonder about the conclusions some descendant of mine might try to make when looking at my own relocations around the USA some 100 years from now.