It's not because they are not trying to portray successful Latinos, it's that most writers, actors, directors and so on are white, so they think in white terms. Yes of coarse there are many Latinos in the business, but most people in Hollywood are white and to a lesser extent African American. Also white people are the prized demographic, white people watch white shows and then go out and buy the products they see advertised. If Latinos were a prized demographic you would see many more Latino shows. Lastly, there is the language barrier.