You can’t blame Mexico. They don’t want them so.....they are facilitating their trek to the US since we’re so willingly letting them all in. And Mexico knows nothing will be done to them for facilitating them. Its a win/win for everyone but the US.
Yes, but Mexico could seal their Southern Border but then they would lose their cut from the Coyotes and Smugglers and Cartels who are probably the real power there.