The logic behind Operation Blockade was straightforward. Placing height-ened security in and around the downtown urban port of entry in El Paso would force undocumented migrants to attempt crossings in more rural areas that were easier for law enforcement to monitor.
Yes, easier to monitor and at the same time there's no one watching them, no one to held them accountable if they did anything wrong. They are the only witnesses and can make up story however they wanted.