People arent climbing walls to enter.

https://www.pewresearch.org/hispanic/2015/11/19/more-mexicans-leaving-than-coming-to-the-u-s/

They are leaving. Americans, even.

https://www.immigration.ca/more-americans-want-to-leave-u-s-and-canada-is-where-they-want-to-go

...

Those who are 'climbing walls to enter' are those from Central America whose countries are f*cked up by US backed right wing governments and their paramilitaries. When you have a choice in between handing over your land to an agro conglomerate backed by US and having to work for dimes for the rest of your life or risk death at the hands of right wing paramilitaries, emigrating to US and climbing walls becomes the better option.