Question

What is most likely the reason an author would refer to a Greek myth in his literary work?

Answer 1

Because it's a recognizable source material and it can be used for telling morals 

Answer 2

Its probably because it is well known so it is reliable and also most people will know what you are talking about because it is like well known and also most Greek stories had a lot of morals and stuff like that so they teach lots of lessons.