It's not. Nobody but the shooter is at fault, in my opinion. I'm willing to bet this was a response to a slew of lawsuits from people that had a lawyer talking in their ear about how a payday is just around the corner and they wouldn't dare fight it because the backlash and blah blah blah.
Whether MGM goes ahead with the lawsuits is another issue entirely. Right now it's all just a shitty situation made worse because lawyers got involved.