You can’t expect to wield supreme power just ‘cause some watery tart threw a sword at you! Burn her! Look, my liege! He hasn’t got shit all over him. The Lady of the Lake, her arm clad in the purest shimmering samite, held aloft Excalibur from the bosom of the water, signifying by divine providence that I, Arthur, was to carry Excalibur. That is why I am your king.