I grew up on the border in AZ. Emigre would pick up any illegal for simply being illegal and haul them back. They even had an unofficial stop outside the kmart in Douglas/Agua Prieta cause it's tough carrying bags back over the fence. What changed recently is the volume, it has become cost prohibitive to keep that many buses going. They tried flying them to Mexico City but that's expensive too, so only felons get that now if at all. I can see why Minnesota might not want to pay the $ to send them back.
Weve had militia patrolling the border for decades too. Detain, hand out cards, radio BP, along come the buses.