ICE is already struggling to find personnel to deploy to this, you really think they keep showing up if they start getting arrested? They don't HAVE reinforcements.
Remember: These jobs suck. The only people doing this are a handful of true believers that actually believe they are achieving something and people with no better options. There is not an infinite pool of people available to do this. When the job gets harder, riskier, or just less pleasant, that pool gets smaller.