Is it not curious that throughout book 5 we’ve seen Athena helping Diomedes defeat the Trojans but in book 6 the Trojans have the idea of praying to Athena to help them defeat Diomedes?
My guess is, Homer wants us to witness the Trojans doing something we know to be utterly futile, which stands for the hopelessness of their situation in general.
It’s funny: we hear the rather lengthy account of the ceremony Hector’s mother is to perform three times, once from Helenus, once from Hector, and once from narration of the actual ceremony, yet Athena’s response to it is given in a single line (311): “She spoke in prayer but Athena turned her head from her.”
.i`` * ^ / . . . . . ` `~ 