Both Al Qaeda and ISIL come from the same place in terms of sunni extremism.
However there is a huge difference in the two organisations.
Even in its diversified form you had to show you were good enough to be in Al Qaeda. Any plans had to be approved but were usually quite professional.
However most attacks undertaken by 'ISIL' are undertaken by lone wolves and we only learn AFTER the event they supported ISIL. In other words ISIL had no input into the attacks but were happy to take the 'kudos' from the attack.
Thus it can be seen attacks these days are much harder to prevent as there is little communication going on. sometimes the lone wolf could be on the radar sometimes they are not.
George Bush has a lot to answer for!