I do not believe that people that only know one language is the majority of the population.

Certainly most people in Europe know more than one language, most people in Africa(poor people) and most people in Asia, most people in South America. Most people from Canada.

It is just people of the USA, because they just can get by with just one language.

But this is like using Imperial Units. The (North)Americans even forced the rest of the world not to use metric, like in aviation(French and Germans of course used meters for it in WWII).