So what's up with suicide terrorists?

It's about turf:

... not driven by religion as much as they are by a clear strategic objective: to compel modern democracies to withdraw military forces from the territory that the terrorists view as their homeland.

The linked Steve Levitt article incisively notes how there are plenty of cheap and easy ways to disrupt people's lives, like highway sniping. Absence of a spate of these would seem to point to the relative smallness of the problem. Of course, if I'm that one out of a million, then it's not that small.