Answer:
Because he believes that Arthur will be England's savior and that his story will grow over the years.
Step-by-step explanation:
Sir Thomas Malory was an English novelist who wrote books celebrated around the world about the legend of King Arthur. Through his works, it is possible to realize that he had a great admiration for this story and believed that it was real and that Arthur would be the savior of England. This is evident when he decides to share what is supposed to be written in Arthur's tomb.
In the tomb of Arthur it is written in Latin "Hic jacet Arthurus, Rex quondam, Rexque futurus" which means "Here is Arhtur, formerly king and future king" with this Malory not only believed that Arthur's story would pass the centuries as he would return to rule in the future being a savior for england.