Are you sure about that? Which Americans are you referring to? There are some Americans practice Shamanism long before converting themselves to Christianity.
Same shytes as Americans participating in Satanism (metal heads), witchcraft (Amish people), and spiritualism (Hippies).
They practice all of those things in the comfort of a country that was built on Christian culture.
In America, many people get away with things that they couldn't in other countries. They can even criticize the president and generate vulgar images of him without going to jail. They couldn't do that to a leader in North Korea or Iran.