No invasion nor occupation of the US planned, no country directly involved, all the terrorists dead.

It looks like terrorism through suicide, is a smart way to get a message across.
Terrorism is the weapon of the weak.
No risk of being prosecuted and tried for crimes (they're dead), the name being remembered (even in bad, but remembered) for a long time throughout the world. Their reasoning is not "I'll meet many virgins in the other side" but could be "We all die one day anyway, so why not do it in a very visible way"?
Just the knowledge of the potential psychological impact can motivate them.
It's time the US studied the pyschology behind a would-be suicide bomber. And , no, they are not "Evil" because that only explains the problem away and doesn't help with the solution preventing it. They are humans who grew up and followed a path and had contacts which, combined, help understand the outcome.
Dealing with terrorism doesn't mean waging war.