Besides not understanding they also don't trust bitcoin, what means they don't have interest for it, otherwise they would have searched for informations regards the matter, concluding it's safe, since you follow all the necessary security measures. Probably americans are comfortable with their currently life standards that bitcoin looks uninteresting for them.
Nearly half of respondents had only heard the names of those coins, whereas 16% said they were very familiar with the cryptocurrencies and 28% said they were somewhat familiar, according to the survey of 1,984 people taken from Feb. 12 to 14.
Anyway, these percentages don't look so low at all. 28% somewhat familiar is a very good indicative.