I think the reality - as infuriating as it is - is that the GOP receives incredible pressure from its business constituency on this issue. Being the "party of business" was always their M.O. Traditionally, insofar as the Dems were the "party of the people", the GOP was the "party of business". In this time of economic stress, businesses want cheap labor. Businesses that are already using qualified, trained, proven illegal immigrants don't want the risk of their illegal status.
Now, with $17 Trillion in debt; 100 Trillion in unfunded liabilities; corporate welfare and bailouts, 10 million fewer people in the work force since 2009, and Tea Party paying attention, there is a conflict between the GOP's business constituency, and their constitutional conservative Tea Party constituency.