It has to make sense from a fantasy perspective.
If Magic Muscle Hero’s warrior bride has her head cut off she has to evoke the power of the sword God to return from the grave to lend a hand once.
If she just grows a new head back for convenience sake that becomes a new established ‘fantasy’ fact you can’t switch off without inventing a new ‘fantasy’ law.Excalibur is purposely returned to the lady of the lake to be returned to the once and future king at the moment when he is needed to return.
It didn’t just fall into the sea.
Yes, exactly. And now the Excalibur/Luke’s-lightsaber has been mysteriously handed down to Rey from unknown, but far from impossible to explain, circumstances.
Also finding a piece of solid metal at the bottom of a pit isn’t exactly comparable to growing a new head.