Boing
That's not necessarily so, they did not seek to announce during the 9/11 attacks who they were, they just did it. Later videos etc. appeared. No doubt the same would occur in a suicide bomb on a airplane. It seems the aim is just to kill as many as possible.
Also in the history of terrorism, and bombings all over the world, by countless organisations, it is pretty standard practice to "claim responsibility" afterwards. Publicity obtained.