simple. NAFTA didn't work because of free trade with China. the business investment that would have gone to Mexico, matching their lower skilled/paid workers with those kinds of jobs, went to china. those jobs going to mexico would have taken pressure off the illegals problem, but american businesses and chinese interests cannot resist the lure of chinese labor.
free trade with china killed NAFTA.
what did that leave us with? it left us with mexico being the source of low cost SERVICE labor for america, but to perform a service job, the physical presence of the worker is required. hence, they came across the border to take those jobs.
Bingo #2. I was in China with a mfg client in '93 - and we were way past the existing economic zone surrounding Hong Kong. It was obvious to all what was happening - there was construction everywhere for as far as the eye could see.
Now imagine the same types of young people (long lost relatives from the Canton region) who comprise 33%+ of the Univ of Calif student body working in low paying mfg jobs in mainland China. Jeez, I still remember them all neatly lined up by their work stations. Pity, Mexicans didn't have a chance.