It's very simply. NAFTA significantly reduced or eliminated tariffs on imports from Mexico, making lower production costs in Mexico even lower, and even more attractive for US transnationals to move production and jobs from the US to Mexico.
And all you have to do for further evidence is look at your first post mentioning the small trade surplus the US had with Mexico in 1992 that is now a $60 billion plus deficit. Unless you think Mexico developed vast new, home grown industries that began selling billions in goods to the US, then what is the only other explanation?
The explanation is US transnationals moving production and jobs to Mexico and also some foreign firms setting up in Mexico to produce products primarily for export to the US.
Automation has gradually increased as a factor, but our starting point is 1993 with NAFTA. And we have larger populations and just more demand for goods now, and products that didn't exist a few decades back, so total industrial output doesn't tell us much without taking into account many other factors, nor does total manufacturing employment.
But it's very simple to conclude that many US plants and jobs did move to Mexico after passage of NAFTA. And nothing you are discussing changes that reality. You're trying to tangle that simple fact up with many other factors that have nothing to do with whether US plants and jobs were moved to Mexico.
There have been many ups and downs in US manufacturing employment since NAFTA passed. NAFTA was one of the downs.
And keep in mind that after NAFTA was adopted, one of Mexico's biggest exports to the U.S. became crude oil ... which doesn't involve much manufacturing employment at all. So the trade deficits were driven by a lot of complicated factors here.
The long story short here is this:
We had $75.5 billion of cross-border trade between the two countries in 1992, and the U.S. had a small trade surplus with Mexico.
We had $557 billion of cross-border trade in 2017, with a $60 billion trade deficit for the U.S.
My question is: Which of these two scenarios is actually better for the U.S.? Would you give up $480 billion of trade to restore a surplus with this trading partner?
Like I said ... I have yet to see an objective analysis of this issue that makes the case either way ... plenty of anecdotes from various industries and/or geographic locations (the article at the top of this thread, for example), but nothing comprehensive that tells the entire story.