Every once in a while I like to pretend that lets say Mexico was the greatest country in the world, with a thriving economy, and more opportunity than I could ever dream of. I then pretend that I live in an overcrowded dangerous shithole of a country that offers me no promise. I then pretend I don't have the resources or necessary know how to legally immigrate. The point of this fiction is to realize how fucking quick my ass would be up and walking to Mexico. Legal or not I would be where the opportunity was. I would crawl there if that presented the best chance for the survival of myself and my family. If I got caught and deported, I would be on the next truck back.
The vast vast majority of immigrants(legal and illegal) fit much more into the situation described above than in any other type of situation. Comparing the difficulty of legally immigrating today vs the immigration of many of our previous generations is just not a fair comparison. Immigration in the 19tg and early 20th century consisted of getting on a boat, and processing when you arrived. It did not cost 15K and take years, you literally got off the boat and poof you were done. There is no one stop daily shop for immigrants today.