The cages were temporary and not a means of internment, which Rump used them for. He needed his photo op to show the immigrants on their way that this would happen to them if they tried to come here.
Gotta hand to that dirtbag, Steven Miller. He was behind all the cruelty and depravity of Rump's immigration policy. Not that he needed him as they both thought alike. Miller was just more intelligent and ruthless.
All the best,
Nonoise