It isn't so much about the fail as to the fact that they can hit us. 
Which is more of the usual pattern of ISIS "growing" by any radical (Shia) muslims willing to engage in violence simply calling themselves "ISIS", than it is any actual ability of ISIS to visit an area, and set up operations. Whether ISIS is simply making claims, these two men "declared" themselves to be ISIS, or if they actually were some product of ISIS networking and outreach... we'll probably never get a clear answer. The current administrations vested ideological interest in downplaying militant islamic threats because it aligns with their broader aims of a third world vs. first world "leveling", and the MSM still carrying water for them, we won't get an honest accounting from the .gov either.
ISIS even kind of acknowledges it with the reference to "lone wolves" in their threats.
When the "branding" of ISIS starts to falter in popularity, or it fractures over disagreements of the finer points of whether a goat or an underage boy is more halal, it's going to vanish almost as quickly as it came into being, save maybe a pocket on the Iraq/Syria border where they actually did "form". The disparate groups across the ME and Africa won't disappear, but "ISIS" will.
