The reason is simple. An actor/actress is what he/she is period. Expressions like "Yoruba actors" fuels that dichotomy which isn't helpful. An actor/actress should be able to interpret roles irrespective of the culture or language. Now, consider this: Why is Olu Jacobs, a Yoruba man, able to interpret roles in Igbo, Yoruba and English movies? Simply, versatility. Be versatile and stop putting yourself in a cocoon or allow yourself to be branded a "Yoruba actor/actress." You are an actor period and should be able to pick up jobs across genres or cultures. Western actors (America, France, British etc) spend up to a year in foreign lands to learn their cultures in order to interpret their roles correctly.
I agree with you completely