Because IS are good at online grooming, which begins with selecting from those they come across - looking for the vulnerable and manipulating them
It can’t be quite the same as the grooming by sexual predators, because the acts they want the targets to commit are so different; but there surely has to be similarities.
IS has not been attacking the West in recent years as frequently as before, but the reasons (hatred of the West and everything it stands for, desire to spread their version of the true way of living, willingness to eliminate others in that struggle) have stayed consistent.
I guess only the security experts will be able to assess if this is one-off, or a sign of renewed capabilities and strategy. And I guess they won’t be making those assessments public