Simple

Yesterday, I quoted Rachel in this post.

One question was:

"Why are all the Mexicans who are willing to risk life and limb confronting the United States government instead of their own?"

Since then, I've realized just how simple the answer is: No risk.

What's the big deal if they do get caught here in the U.S.? Do they get deported? Hell no. Unless they have at least one felony conviction, they don't get looked at twice.
An exception to that rule may be that some I.N.S. agent gets a bug up his ass to make a showing or maybe a quota. They may drive past the construction site and fill the paddy wagon up with injured or crippled up illegals who can't run as fast their healthy co-workers. But outside of that, nah. They're pretty much safe here.
That has been proven tirelessly.

The law is forbidden to do any sort of background check on someone unless they are a U.S. citizen (hat tip to the Fucked-up A.C.L.U. for that), so what are they afraid of? Not a gawd-damn thing. And even if there were any sort of background checks, the law would be looking at some dead dude's info since any sort of identification the illegal would have is most likely stolen anyway.
They can get caught over and over again. No recourse.
And as Mark points out, they have the law on their side if they happen to get hurt by U.S. law enforcement.

Now on the other hand, everyone - including Mexicans - knows just how fucked-up Mexican prisons are or can be. Maybe not from personal experience, but we've all heard the stories. In and forgotten. Definitely no so-called 'Blind Justice' system there. And they aren't all that concerned with fair treatment for prisoners.
When was the last time you heard of a prison riot over some fucking peanut butter at a Mexican prison?
Yeah. Me either.
And don't even think about some laughable A.C.L.U.-type group of happy-asses down there looking to help out a fellow citizen who's down on his luck.

Now if you have a bit of cash on hand for 'bail', you may not end up in jail, but the average Mexican ain't got that on hand or they wouldn't be trying to sneak in here, now would they?
Hell's sake. You can't even drive a car down there without a pocketful of twenties to give to the nice officer as 'bail' for some bogus traffic violation.

But I digress.

The point is, in Mexico, they very easily could get sent up for who knows how long, or they may just end up shot. Here, they don't have to worry about a damn thing other than at worst, losing a day on the job getting run through the system. And eventually, they'll get absorbed into the system and become what amounts to - if not - an American.

So, a days' wages or a life sentence for confronting the law: Which would you choose?

It's not like these people have a choice. They sure as hell have no freedoms there.
Unlike our founding fathers who were able to take up arms against their oppressors, Mexicans ain't. They have been disarmed. They've been beat down and overtaken by their government. Their government is 'taking care' of them now, like libtards and socialists would have our government take care of us. After all, we're not able to take care of ourselves, now are we.
They know they're not taking on the entire government here. And they don't have to fight. All the hell they have to do is come in under the radar and they're pretty much set for life..