It may have been reluctance more than anything. With all the pressure put on law enforcement lately, what would have been the blow back if they went in early and ended up in a firefight at the guys house?
I mean, that's their job and it's not really those kinds of things that have lead to law enforcement getting bad publicity lately. It's excessive use of force, biased policing, an us against them attitude toward the public in general, and targeting minorities that has been the issue. And, frankly, the fact that this guy posted what he was doing to do along with when and where, and law enforcement did nothing about it makes it look even more suspect in term so of biased policing and targeting minorities. I doubt many would have an issue if they went in to arrest this guy and it resulted in a firefight after people saw what he posted on 4Chan. These are the things we need Police for and this is clear probably cause with exigent circumstances. Yet, they did nothing either because they somehow did not know about it or because they didn't care.