"I am still curious as to how and why this has become such a hot issue when these illegals have been here for so long."
Guestworker Program (Pronounced Amnesty)
1) 9/11 brought an intense focus to national security (at least by American patriots). ...so the issue has been building steadily since that time. It's no secret now that tens of thousands of people from nations that sponsor terror - Arab/Muslim countires - have been apprehend at the border since 9/11, and most estimates are that 4 to 5 times that many actually make it into the country undetected.
2) Although illegal aliens have indeed been here for a long time, the numbers have grown expontentially over the last decade or two, and have now reached numbers that are impossible to ignore and put a huge strain on the taxpayer. Illegals get free education, medical, and they bring in third world diseases that cost a lot to treat.