I agree and I'm wondering why no one has ever challenged this. It should have been done years ago.
The United States Supreme Court is made up of attorneys approved by the American Bar Association (the ABA.) It is the most liberal organization in the United States save of the Communist Party USA.
Additionally, the United States Supreme Court is made up of Jews and Catholics. They are in no hurry to change standing precedents and break up families over minor immigration infractions. Their commitment to keeping families together is a bit more pro-family than anti-immigrant.
Finally, changing standing precedents is not a popular subject. It's how we changed from a Republic to a Democracy. The United States Supreme Court would rule one way, public opinion would change and the high Court would change their own precedents to appease the public. George Washington (in his Farewell Address) warned against this practice:
"It is important, likewise, that the habits of thinking in a free Country should inspire caution in those entrusted with its administration, to confine themselves within their respective Constitutional spheres; avoiding in the exercise of the Powers of one department to encroach upon another. The spirit of encroachment tends to consolidate the powers of all the departments in one, and thus to create whatever the form of government, a real despotism. A just estimate of that love of power, and proneness to abuse it, which predominates in the human heart is sufficient to satisfy us of the truth of this position.
...If in the opinion of the People, the distribution or modification of the Constitutional powers be in any particular wrong, let it be corrected by an amendment in the way which the Constitution designates. But let there be no change by usurpation; for though this, in one instance, may be the instrument of good, it is the customary weapon by which free governments are destroyed."