The US immigration system turning legal vs illegal immigrants against each other is by design. There's no reason the system has to be so broken that millions feel like coming illegally, living on the margins, and risking deportation is a more feasible option than attempting one of the purposefully cumbersome, overly bureaucratic routes.

Anti-immigrant Americans and their elected officials understand that they can probably never close off the US to immigration entirely, due to our nation's history. But they're more than happy to never compromise in order to fix the system, and they definitely love the animosity the systemic dysfunction sparks between different immigrant groups, their families, and their communities. It quite literally helps keep xenophobic politicians in office, or gives them a cultural wedge issue to use in campaigning even if their jurisdiction is nowhere near the border.

Edit: phrasing