They're heavily latino because you can't pay people to move to the Rio Grande Valley. They only people working there are the people from there. The police aren't an occupying force like they are in the urban areas of America.
I've lived in two of these areas, in El Paso, TX and Arizona. I'm familiar with the Rio Grande area. I've never been to Houston or Miami area so I can't speak on them. I've worked with a ton of Mexicans from these areas and I'll try to explain.
I knew there was no chance Texas was going to go blue but when I saw Arizona was close, I thought there might be a chance and I'll explain way. I thought with the mass shooting in El Paso, the vote would have been more democratic in Hispanic Texas but I'm not surprised. El Paso And Rio Grande are about 900 miles apart and culturally very different.
If you are latino and you live in the Rio Grande Valley, everyone looks like you. The mayor looks like, the police look like you, your doctor looks like you and your teacher probably looked like you. The majority of the middle class in that area looks like. There's a reason for that. White people don't want to live around you. White people would rather live in bum fuck Idaho or Wyoming than live in area in which they're the minority. A lot of the families have been there forever, were never immigrants and actually look down on the Mexicans from the other side of the river. Here they differentiate between Mexican-American and Mexicans. If they happened to have family in Mexico and want to visit, it's just a short dive and they cross the border just like any other country in the world. Culturally they wear cowboy hats, drive pick ups and listen to country-western music. In no way does this excuse the racism these people are. The look at black people and believe what the white man told them. That's whysome vote republican and are not as heavily democratic.
If you live in Arizona, it's a whole different story, especially the Phoenix and Tucson area. Unlike Rio Grande Valley, white people want to live there and do what they can to keep them from entering their spaces. The mayor doesn't look like and probably got elected talking shit about you. The police don't look like you and the sheriff was elected for talking shit about you. There's the "where are your papers laws", basically stop and fisk. Your doctor and teacher don't look like you and the school were zoned to keep you out. Unlike Rio Grande area, a lot of people are from immigrant families, a lot closer to their families still in Mexico. Here, all hispanics are the same. If you want to visit family in Nogales, you cross the border like in Texas but on the way back to Phoenix you have to get through 2 Border Patrol checkpoints where your car might get searched again and you're basically interrogated again. The highway from the border to Phoenix is heavily patrolled by the Border Patrol and the Arizona state troopers. Just about every 10 minutes, you'll see a car pulled to the side. The highway is a fucking gauntlet. The Border Patrol has turned many of the communities into demilitarized zones. ICE has a much heavier presence there also with raids occurring daily. It can be like the modern day version of Jim Crow. Culturally they're chulos, driving honda's and listening to rap.
I would agree that the Dems shouldn't use too much political capital on the latino vote. You're going to take California anyway. For the next decade or so, latinos in Arizona should just be happy Trump's next in office anymore.