It’s not just Mexico - the illegal immigrants come from Central America and are just passing through Mexico from the Socialist countries to the South. Mexico was letting them pass through as long as they promised to keep on moving. Thanks to Trump, Mexico even tried to stop them, offering them employment, housing, etc., And finally attempting to stop them on the southern border of Mexico.
It didn’t work because there are simply too many and they have funding from the international left and the criminal gangs that make a living off them.
But mostly, they won’t stop coming until the Socialist regimes - particularly Maduro (VZ), Raul Castro (Cuba), and Ortega (Nicaragua) - have been wiped out. That’s why they’ve got to go. This is endangering the US.
You’re very easy on Mexico. By the way, it’s also a socialist country. And full of criminal corruption.