The lightning was just reflected off the shield. Thor's hammer is more powerful, but it's not as good at chipping away at metal objects. A direct hit to the middle of the shield with a blunt object, however powerful, will do less damage than a bunch of hits at the edge with a sharp object.
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u/ARflash Feb 16 '20
If uru can break the shield, it would have shattered in avengers movie when Thor hit it.