While I'm sure there's some degree of corruption/collusion I think its also just the realities of quotas: if you get the same quota points for an armed human trafficker as you do a peaceful grandma, who are you going to pick next to deport? Who is going to take less time to pick up?
The quotas are actually one of the reasons protests are so effective as well. The more time they waste the worse the ICE agent's numbers look.