Illegal Immigration is a false issue.
More Mexicans, for example, are LEAVING the US compared to coming in:
http://www.pewhispanic.org/2015/11/19/more-mexicans-leaving-than-coming-to-the-u-s/
It's practically non-existent now, and remaining immigrants (who have mostly been in the US for decades) affect only a few industries meaningfully.
Hillary supports free trade, so that means more jobs for poor people in their own countries. So in a sense, you're right; why would uneducated people immigrate to the U.S. when there are no manufacturing jobs there for them, and they can get jobs in their own countries? Likely we will continue to see an exodus.
The main demands for immigrant labor are:
1. Agricultural work, for which we already have extensive temporary visa programs for (these are not largely illegal immigrants, although illegal immigrants make up a large portion)
2. Nursing, like agricultural work, It's relatively easy to get a working visa for a nurse due to the high demand and pressure from retired and medical lobbies, but these people are well educated. We would be idiots to turn them away given how badly we need more nurses.
3. Food and cleaning services. This sector is shrinking and being mechanized -- e.g. automatic dishwashers, centralized food processing and distribution. This is the top job for illegal immigrants currently, and it's going to vanish very soon.
http://www.slate.com/blogs/business_insider/2016/05/27/mcdonald_s_ceo_says_chain_will_use_robots_in_the_future.html
Automation is cheaper and more efficient than any living wage worker. Jobs are shifting to solely face to face interaction, and for that these companies want bright eyed young Americans. Immigrants have always been mostly hidden in the back, and now those jobs are being replaced.
4. Construction, the second most common; hired by shady contractors trying to save money, or stingy rich people like Trump. This is one area that could be cracked down on, (although I don't agree with cracking down on it). Mostly by unions, which are "good at" complaining and leveraging political power to get things changed. We won't see construction robots for a while yet.
Here's a little more insight:
http://www.pewhispanic.org/2015/03/26/share-of-unauthorized-immigrant-workers-in-production-construction-jobs-falls-since-2007/