It seems that the FBI didn't do the takedown in the typical manner as they have with Islamic radicals in the US. In the majority of those cases they have used undercover operatives to act as fellow supporters and provided access to "explosives" and materials to make a bomb, then carefully lead them down the path. In many of those cases, the defendants would not have had the means or ability to get the plot any further without the help of the FBI. One or two cases have been thrown out because of that.
But with this one, the people were fully capable, and had progressed to the point of getting ready to move on their plans. That makes this a very worrisome case indeed.