Look at the numbers. Trump is a dumb turd, but surely some saavy Republicans pulling strings must realize if you just grant these people citizenship they end up voting Republican.
That would only be advantageous if you valued democracy. The only reason the GOP cares about elections is because they need to win them to install an authoritarian. A group of minorities to scapegoat is much more valuable to the GOP project.
Scapegoating them is one thing. Actually deporting them is another. The people who employ illegal immigrants are doing it so they can pay them a pittance and have leverage over them. They're not going go want their cheap workforce deported simply because it'll increase costs.