The inspection didn't require them to remove the part to look for cracks - they were to look at the bearing in place and verify that the two halves hadn't separated, by confirming that the outer edge of the bearing was still in line with the housing.
The explanation seems to be that the failing of this bearing doesn't mean that the engine will fall off, because all the parts are retained, with the inner race inside the circular lugs. But it will make space, which means the mount will rattle, and if that is combined with existing, unobserved cracking in the lugs, could have lead to rapid progression of those cracks and a failure before the next inspection occured.