This is America's very basic race/ethnicity breakdown, as of the 2010 census:
I want to divide "representation" into 2 camps: racial discrimination, and Hollywood whitewashing.
I know you were not asking about the Black Lives Matter movement, but I feel that this topic cannot truly be discussed without the addition of BLM.
While the Latino population faces a high level of police discrimination, it still pales in comparison to the issues of violence against blacks in America. From PBS Newshour:
Among minorities, the rate of police killings for Latinos is second to those of African-Americans. As of today, an estimated 94 Latinos have been killed by police in 2016 alone, making up 16 percent of the 585 police-involved killings this year. In contrast, people who are black or African-American are only 13.3 percent of the U.S. population, but 144 black Americans have been killed by police in 2016. At 25 percent, those deaths represent a disproportionate number of officer-involved fatalities compared to the population.
There is a movement called Latino Lives Matter, but they do not get as much media coverage as the Black Lives Matter movement. Many Latinos have spoken out in favor of the Black Lives Matter movement. Essentially, "Black" is being used to denote all minorities within the movement and their struggles against systematic oppression. It helps that "of the 57 million Hispanics living in the United States, about a quarter [or about 15 million people] identify as Afro-Latino [mixed race Latino and African descent]" (source), and therefore feel that they can relate to the oppression that many blacks are undergoing at this moment.
When talking about Hollywood whitewashing, take a look at this graph below:
Hispanics are actually the only group within Hollywood whose representation is not representative of America as a whole; the ratio of blacks in film to blacks in America are about equal, as are Asians and "others" (Native American, Pacific islanders, mixed races, etc). However, less than 5% of all major Hollywood actors are Hispanic, and this leads to what is called "Hollywood white-washing."
Many directors want the most noteworthy actors in their movies in order to get the most recognition for profits and awards. It's how you end up with Andrew Garfield playing a Brazilian-born tech mogul in The Social Network, and Natalie Wood playing Maria (and totally botching a Puerto Rican accent) in West Side Story. If you want to learn more about white-washing across all races, check out "Hollywood Whitewashing: How is This Still a Thing?" from Last Week Tonight.
One theory about why they do not receive as much coverage is that there are simply more pressing issues in the Latino sphere to worry about. Donald Trump's campaign, increasingly restrictive immigration laws, and the fact that Mexicans make up over half of all estimated illegal immigrants are all incredibly important problems within their community right now. This is probably one big reason there is less push for more Latinos to represent the ethnic group within Hollywood. I'm not saying that they cannot work on two issues at once, but when nearly 10% of a large group are under danger of being found, reported, and deported because they have outstayed a visa, it is understandable that some people would be scared of "rocking the boat" too much. I do believe that pushing the Black Lives Matter agenda further into acceptance within the public eye will help all factors of under-representation for all minority races within our country.
Or hey, it could all be a plot created by Salma Hayek in order for her to get the most award-winning rolls in Hollywood. Which sounds more reasonable to you?