Malory had a clear bias when it came to Lancelot, who is a major character in Malory's Morte D'Arthur. The work details the love triangle of King Arthur, Lancelot (one of his knights of the Round Table), and Guinevere (Arthur's wife).  Lancelot and Guinevere began an affair without Arthur's knowledge, but he later found out about it.  The work ends with the deaths of Arthur and later, Lancelot and Guinevere.  Arthur is mortally wounded by his illegitimate son, Mordred.   Guinevere dies of heartache, and then Lancelot dies after Guinevere's passing because he is absolutely devastated about Guinevere's death.  

When Lancelot dies, despite the fact he had an affair with Arthur's wife, Guinevere, Malory writes of Lancelot as a huge hero who was honorable and just, the best knight at the Round Table.  Despite the title, Malory sings the praises of Lancelot moreso than Arthur, really.

What is Malory's intent in writing Morte d'Arthur?

Morte D'Arthur details the story of King Arthur, Lancelot, and Guinevere.  It is a sweeping story of Camelot, the Knights of the Round Table, a love triangle, and betrayal. 

We can only speculate about the intent of the author; however, Malory had a clear bias as it relates to Lancelot.  He admired his character, and this becomes evident in this work. Despite the fact that Lancelot betrays King Arthur by having an affair with his wife, Guinevere, Malory sings Lancelot's praises when he dies, writing about the fanfare surrounding Lancelot's funeral and discussing how Lancelot was the greatest knight of the Round Table...a man who possessed great skill and who was true and just.  It appears one of the intents of Malory's work was to not only tell the story of Arthur, but to sing the praises of Lancelot.