Because Republicans and conservatives for the most part are compassionate and would not want to visit the sins of the parent upon the child. This would be particularly the case of children who have been in the US a long time and would be sent back to a country where they do not even speak the language.
Now you seem to be viewing this as a voter issue ala the Dims. Dims do not have compassion and thus only want immigrants who will vote Dim. We Republicans and conservatives are better than that and don’t want to visit the sins of the parent on the child.
Of course the devil will be in the detail. How long must a child have been in the US to qualify. What status will such people have? That is resident alien or citizenship or what? What actions of the child are disqualifying, ie felony convictions etc. Is English a requirement etc.
Stop spending money.
Smaller government, not bigger government.
Take your compassion insults and stick them under the pile of debt that is destroying America.