Considering that they’re trying to use self-constructed materials, attempting to fabricate something that will pass through security (and in the two cases the OP cites, did do so successfully), are working with highly unstable and touchy chemicals (such as undiluted hydrogen peroxide, which will set your clothes on fire if you spill it on you), and are ultimately going to kill themselves in the process of triggering the bomb, I’d have to say that they’re not “incompetent boobs”, but unlucky and perhaps insufficiently trained.
The fact that they got the “getting explosive and incendiary substances successfully past intense security” part down pat gives me sufficient reason to be concerned about them, thank you very much. I still con’t get large quantities of bottled liquid or the scraper I inadvertently left in my briefcase past the checkpoints.