Actually, more Mexicans are leaving the US than entering it

Well, here's something I hadn't realized. Maybe it's a fact I should have been aware of, but apparently, in recent years, more Mexicans have been leaving the USA than have entered it, and the estimated number of Mexicans in America, both legally and otherwise, has been shrinking throughout the administration of President Obama.
According to a 2015 report by the well-regarded Pew Research Centre, between 2009 and 2015, over a million Mexicans moved back to Mexico (mainly to reunite with families, or to start a new family, or because they found jobs there, although about 14%  of them were illegal immigrants who were deported). This compares with about 870,000 new immigrants over the same period. The total number of Mexicans in the USA in 2014 was about 11.7 million (including 5.6 million who were there illegally), compared to 12.8 million at its pre-recession peak in 2007 (including 6.9 million illegals).
So, maybe Donald Trump's "big beautiful wall" is actually really to keep IN the Mexican immigrants who keep much of the country running.