Most of my friends from high school who didn't go to college went directly into these fields and did well. Now the fields are filled with low wage but experienced illegal aliens who have driven the base wages for these professions down so low that it is pretty much impossible for young people to make a career out of these jobs.
And what is amazing is that the Unions support bringing in these illegal aliens. It proves that their goal is not better working conditions for their workers, but power and money through numbers.
There are about 23 million immigrants in the labor force with about 8 million being illegal aliens. You keep mentioning illegal aliens as the cause and miss the elephant in the room—legal permanent immigrants. And add on top of that the 2 million guest workers at any one time who are in the workforce. The scarce jobs are going to immigrants, legal and illegal.
Although if the illegals are unionized and their wages lifted to that level, they won't be such a bargain to employ anymore. That might help.