Why do americans don't consider dominicans as multiracial people?

The only blacks are the dominicans in the coastal areas and the haitians immigrants as black immmigrants from other island. they are a lot of whites in the central part. However, the vast mayority of dominicans are multiracial( a mixture of spanish,taino and african) there is a lot of diversity, why do some people think sammy sosa and david ortiz are "average" dominicans when in fact they are aliens to us, most dominicans are mixed. mixed equals mixed, deal with it. I don't know why so many people in the US still believe in the one drop rule when white americans used that to increased the number of slaves. in the dominican republic mixed people were never slave and some mixed people despised blacks