"Is cycling that popular in America?"
Cycling is not very popular in the United States. In fact, most people are indifferent to cyclists at best and despise them at the extreme viewpoint. Our society is built around the automobile and bicycles are an impediment to the motor vehicle.
"I have always thought it was more of a European and Asian thing, and that Americans would prefer buses, cabs, or private cars rather than cycling to their destination."
Your thoughts are mostly correct. We prefer personal transportation to public transportation as a rule and any form of motorized transportation over human-powered transportation.
"That's why most of the professional competition are in Europe and rarely in America, so this is really a surprise. Do you think cycling would ever be as popular in the US as it is in Europe or Asia?"
I doubt cycling in general and road racing in particular will ever be as popular in the United States as it is in other parts of the world. Despite the fact that America is a very large market for cycling products, the sport, itself, is very small here. We do have some very good races, but when compared to almost anywhere else that has a cycling culture we are considered third rate.
American do love to compete and win. If there's money and fame involved we will be there, if only in small numbers. Among the general population, competition on a bicycle generates insignificant numbers.
"I'm curious, since all you guys do there is run in marathons and stuff."
The United States has a pretty decent participatory record in 'some' sports. Cycling is considered something children do. When our children get to the age of 15 or 16 the motor vehicle becomes the preferred method of transportation. Almost any activity other than cycling becomes the preferred means to stay healthy and fit...if that path is chosen.
