From my understanding, its because they are enforcing the laws with zero tolerance. Those same laws mandate the separation during the process. Another exacerbating circumstance is HHS and DHS have little to no coordination, other than DHS saying "here you go" and turning over the kids while the parents are incarcerated. This has been the law for a while I think, going back to the 80's maybe? Its just in the past, DHS just said "gimme your names, and come back for a hearing." Now they aren't, which has exposed a fatal flaw (among other things).