After the boom of the 1960's and 1970's Mexico's economy has been in a relatively poor state since the 1982 meltdown--recovery from which was slow well before NAFTA. NAFTA has not cured Mexico's problem of slow growth, but it did't cause it, and it is unclear that it made it worse (overall) than it otherwise would have been. For an alternative explanation:
"Yet it seems that, at the end of the day, the reason why post-NAFTA Mexico has failed to grow comes down to something much more fundamental: a fear of growing, embedded in the belief that the collapse of the 1980s and early 1990s (including the devastating “Tequila Crisis” of 1994-1995, which resulted in a another enormous devaluation of the peso after an initial attempt to contain the crisis was bungled) was so traumatic and costly as to render event modest efforts to promote growth, let alone the dirigisme of times past, as essentially unwarranted. The central bank, the Banco de México (Banxico) rules out the promotion of economic growth as part of its remit—even as a theoretical proposition, let alone as a goal of macroeconomic policy– and concerns itself only with price stability. The language of its formulation is striking. “During the 1970s, there was a debate as to whether it was possible to stimulate economic growth via monetary policy. As a result, some governments and central banks tried to reduce unemployment through expansive monetary policy. Both economic theory and the experience of economies that tried this prescription demonstrated that it lacked validity. Thus, it became clear that monetary policy could not actively and directly stimulate economic activity and employment. For that reason, modern central banks have as their primary goal the promotion of price stability” (translation mine). Banxico is not the Fed: there is no dual mandate in Mexico.
"The Mexican banking system has scarcely made things easier. Private credit stands at only about a third of GDP. In recent years, the increase in private sector savings has been largely channeled to government bonds, but until quite recently, public sector deficits were very small, which is to say, fiscal policy has not been expansionary. If monetary and fiscal policy are both relatively tight, if private credit is not easy to come by, and if growth is typically presumed to be an inevitable concomitant to economic stability for which no actor (other than the private sector) is deemed responsible, it should come as no surprise that economic growth over the past two decades has been lackluster. In the long run, aggregate supply determines real GDP, but in the short run, nominal demand matters: there is no point in creating productive capacity to satisfy demand that does not exist. And, unlike during the period of the Miracle and Stabilizing Development, attention to demand since 1982 has been limited, not to say off the table completely. It may be understandable, but Mexico’s fiscal and monetary authorities seem to suffer from what could be termed, “Fear of Growth.” For better or worse, the results are now on display. After its current (2016) return to a relatively austere budget, it remains to be seen how the economic and political system in contemporary Mexico handles slow economic growth. For that would now seem to be, in a basic sense, its largest challenge for the future.
https://eh.net/encyclopedia/the-economic-history-of-mexico/