I think most of the adults at ICE and the like are working on counter terrorism issues. Just listen to the Rats. They scream about containers and this draws resources to the ports. Does it hurt issues that we worry about? Sure, but Pedro is not planting IEDs in your flowerbeds.
If we keep getting run in circles by politics we will not get anything under control. Local municipalities could help out too but, no one will help until they get a slice of the DHS grants. As long as we tolerate 'enforcement free zones' this interior problem will not go away.
Question for you though. How are the comparisons for actual crossers caught in the border regions? Seems like the asset shift, post 911 may have put more agents in these areas. That might explain some of the interior drop also.
Another issue I wonder about too. Does work place enforcement hurt employers disproportunately? (I am not defending the scum, however if you allow/encourage illegal immigration, does that not force business to use the cheapest labor?) This whole picture would likely appeal to Rats since they hurt/punish business and create a victim class who are waiting for a socialist type rescue/voter registration. That means we should expect the Rats to push work place enforcement exclusively, giving clear support for your numbers.
Fix the border is the best solution, then clean up the mess.
You have to both secure the border AND provide interior enforcement to fix the problem. Encouraging border intrusions by promising amnesty and rewards only makes the problem worse.