Assuming they were intercepting the G/S from above, faster than they would needed to be, they were naturally EXPECTING the somehow longish and gradual slowing down, hence the apparent inattention to speed parameters until it was too late; they’re attention to speed (as well as fmgc modes, engine parameters) was turned into another direction, probably because they knew it would take some time for the speed to drop to a reasonable value.
Their minds were for some strange reason occupied with some other thing that they’ve felt more important to deal with. That’s the real mystery here.