Actually, they were leaving voluntarily during 2008-2009 because new jobs were essentially non-existent in the U.S. at that time.
And since illegals come to this country for jobs, wouldn't it make more sense to invest the "wall money" into the countries that have the most illegals that enter this country? Sorta like Israel's $3-$6B yearly subsidy the U.S. gives them, but with a purpose.....like stimulating their economies so they stay home vs. trying to get to the U.S. for the low level jobs here. If we can afford billions per year building and maintaining a useless Maginot Line wall, wouldn't the money be better spent at the source of the problem instead of using the money as a band-aid solution that'll prove useless in the long run?