You mean like they DIDN'T do with 9/11?
Or perhaps that attack wasn't big enough to merit the effort to stake their claim to fame?
While it's true that OBL did fess up to it, I seem to recall the venue being a private tete-a-tete (a scumbag to scumbag tea), which was videotaped for posterity (rather than distribution). IIRC, the tape was found in a safe house our guys knocked over.
This was a year or two after the fact.
It wasn't until well after that inadvertent release that they openly took credit for the attack.
But, maybe you're right. Maybe 9/11 just wasn't a big enough deal for them to care one way or the other about taking credit for. That must be the case, if your logic holds any water at all.
Just as a note to this discussion, I remember Osama supposedly saying (right after) he WISHED he could take credit for it.
Maybe it was just so big even he was AFRAID to admit it at that point?