Simple: it doesn't punish brown people.
The solution for the vast majority of illegal immigration is simple: Focus on employers. Its like with a drug problem.....you don't focus on the users. You focus on the suppliers.
Make it mandatory to use E-Verify with hard jail time (min 1 year in federal prison) if an employer doesn't use the system when hiring someone. If a perspective employee is put through E-Verify and passes....then the employer is completely covered, even if later the employee is found to be an illegal.
Focusing on the illegals is just stupid policy. They are hard to find. They move around. We don't know their name. There are so many of them. And if you deport them, they can come back.
Focusing on the employers who hire illegals makes much more sense. They're easy to find (they usually advertise), they stay put in the same location, we know who they are, and there are far fewer employers than the illegals they hire.
And best of all, the E-verify system already exists. Just a legislative hip check on making it mandatory, a few dozen high profile prosecutions of employers who ignore the law.....and the supply of jobs for illegals will overwhelmingly dry up. And without work, illegals will most often deport themselves.
We could literally resolve the overwhelming majority of new illegal immigration by this time next year. But Republicans would never go for it. As they don't really want the problem solved.