All or almost all of that info can be pieced together from facebook, online or physical phone books and other information sources.
The “why” and “why them” it is being collected it are the bigger issues.
It is a well-known communist agenda to go after the police, that is why. Some far right paranoid militia types agree: it's what I call "far right meets far left."
Anyone who followed this particular police operation to evict the Occupy L.A. vagrants after TWO MONTHS of tolerating their camp-out, knows that it was one of most delicate, downright polite maneuvers conducted by ANY police department in a similar situation ever. The occupiers/arrestees have no grievance whatsoever.