Or maybe because they are illegal?
Most of the illegals in my area try to fly under the radar as they have good oil-patch jobs, work hard and keep their noses clean. I have no idea how many of them have legitimate documents but since they can get NM driver's licenses that's a start. On some jobs I supervise, the foreman speaks English but gives instructions to his crew in Spanish.
More importantly, they have families where the little ones are US citizens and are rapidly coming into the public school system. In four years our school enrollment has pushed us from 11th to 8th in the state and this year we saw an increase in over 500 new students from the previous year. We are building two new elementary schools that will open next fall and are waiving a master's degree requirement for new teachers.