Why did the kings of England want to be decedents of King Arthur?

Answer 1

Arthur was a major part of English and British culture, and, it was believed, history. It was said that Arthur was the saviour of the British people, and all the records and stories available to the public claimed that when he was the king of Britain, the boundaries of the kingdom (an empire, under his hand) stretched farther than ever before or since.

For an English king to claim descent from Arthur would be a major propagandist move, intended to endear him to the public and have them see him in a similar light to Arthur. During the Tudor era, however, belief in Arthur as an historical figure began to fade out of fashion, and though he maintained his importance culturally, it was as a mythical hero, not a someone who ever actually existed. Anyone to claim descent from Arthur after the Tudors would have been laughed off the throne; indeed, Queen Elizabeth I (the final Tudor monarch) is believed to have burst out laughing at the suggestion by a courtier that she was of Arthur's bloodline.