While I'm sure that in reality terrorism is rather a great political leverage than a biggest threat, it also has one specific property that HN should be familiar with: scalability. Hurricane, shooters and road/cancer deaths are not scalable, i.e. they cannot be over-produced because it's just weather, psychopathy* and other statistical accidents. Terrorism though can be scaled by orders of magnitude by pretty simple means.

* terrorists can be viewed psychopats, but let's leave that question open, since it is more military than civil.