I think they don't want people to realize how depraved the teens are. For one thing, if you don't get a name, you won't know if they've done it before. Multiple events could come from the same anon. And of course the whole Coulter's law. Blacks are going to be hugely represented, and if people knew what the criminals looked like they'd be even more suspicious of young black men than they actually are.

The real tl;dr is that they're more concerned with protecting criminals than victims.