Why did TV and movies portray cowboys as mostly white?

Actors in Westerns were played cowboys. Why is this true since the original vaqueros were of Hispanic descent ?

movies are made as entertainment for the masses not as historical records

I agree with justadude. All movies are made with the intent of ringing the cash register. Even the history textbooks have to appeal to the school boards that select them or they will never be sold. For that reason, the viewpoint of historical events are often very different in the history of two countries that were on opposite sides of the event.