Half of the reason has been the incompetence of the terrorists. There have been a number of failed attacks in the US in the last few years: <a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;List_of_unsuccessful_terrorist_plots_in_the_United_States_post-9&#x2F;11" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;List_of_unsuccessful_terrorist...</a>