Yeah, our elected officials see how easily manipulated the uneducated illegal alien population is and they salivate. The state of affairs in Mexico with the protected ruling elite class is the goal they have for the US.
Others (Dems) see the influx of illegals as a current and future political asset and guarantee of permanent political power. If they can paint the GOP as anti-immigrant and anti-Hispanic, then the Dems will lock up the biggest and fastest growing minority in the country. Currrently, one out every three Dem voters is either black or hispanic.
Some (GOP) see the influx of illegals as a source of cheap labor that can be exploited and controlled and without any real leverage in terms of worker rights and benefits. It also dampens wages paid to American citizens at the lower end of the wage scale.
Finally, there are Dem and GOP politicians who represent states/districts that have a substantial hispanic population. They want to stay in office and the way to do that is to pander to the hispanic groups. It is interesting to note that some of the GOP reps who voted against the House bill included JD Hayworth, Ros-Lehtinen, Lincoln Diaz-Balart, Heather Wilson, and Chris Smith.
When you have such a large coalition of Dems and Reps who don't do anything about illegal aliens except to make them legal, then they can ignore 80% of the American public.
The question is: why are our leaders not doing anything about illegal immigration, Mexicans (to the tune of 10,000,000 here and 10,000 arriving daily) in particular?
May I suggest the answer is: on the whole, they don't know what the he11 to do about it. While money & votes & power play some role in the answer, fact is that ten million (maybe 30M) people are not easily located and deported without severe impact on society. Illegal immigrants believe they have a right to be here, have a need to be here (as the Mexican economy sucks rocks), and are now binding into a unified force he11-bent on staying. Removal won't be pretty, to say the least.
Witness the consequences of trying to eradicate enemies from Iraq, Afghanistan, Somalia, etc. - when the enemy is entrenched in an otherwise (and more-or-less) friendly population, eradication is extremely dangerous, tedious, exhausting, and destructive. The "Reconquista" crowd and their hangers-on is large, and largely indistinguishable from the general population. Actively arresting and seriously deporting illegal immigrants may very well result in active resistance amidst a sympathetic populace. This will escalate into a concerted, protracted, and violent hunting of the "he11 no we won't go" invaders. Active border sealing and deportations will polarize the political spectrum, galvanize those supporting the presence of illegal immigrants, go from "fighting for rights" to actual fighting, and start a hybrid civil and international war.
Our leaders don't take well to noncombatant casualties in overseas conflicts. They are far less willing to risk collateral damage and casualties on our own turf and among our own people. The recent Reconquista demonstrations ("A Day Without Immigrants" et al) make it clear that illegal immigrants are serious about staying here, and taking "here" by force if necessary (the "Aztlan" movement). Even if most illegal immigrants are just here to labor for a buck, threatening what they perceive as their own meager existance strikes a dangerous chord in the human psyche, and being human they will ultimately fight for access to the sources of providence they consider theirs. Threaten their source of income, paltry as it may be, and you threaten their existence and that of their families - that's a huge motivator for war. Tell ten million people that they are going to leave, by choice or by force, and a serious percentage is going to physically fight deportation.
War is about making life so unpleasant (or nonexistant) for your opponent that he will comply. The face-off is rapidly becoming: national soveriegnty & rule of law & rights of citizens, vs. making a living (mundane as it may be, it's better than untenable Mexico). The two sides are, from their own perspective, vital. If one is pushed too far, the other will fight back. The latter is pushing, and pushing hard; the former is trying desperately to avoid the unavoidable: war.
Our leaders do nothing because doing something will lead to American soldiers in American cities destroying American property and killing people of both nationalities (deliberately or not is irrelevant). Sealing the borders and deporting the invaders will, considering the huge numbers involved, result in lots of casualties and collateral damage. Law only exists because of cooperation to avoid violence; the invaders are not cooperating, so violence is the only route - and our leaders desperately want to avoid violence, lest they not be re-elected.