Why did roman artists deviate from the Greeks' portrayals of mythological events?
There are many reasons why they did it. Mythologywise, in the
war of Troy, there were gods who were besides the troyans
(Aphrodite, Artemis, Mars...) and who were against them (Hera,
Athene, Poseidon...). Since Aeneas was troyan, and his descendants
were the Romans, Roman people considered the 'antagonist' gods bad,
but they respected them too.
In another aspect, there were some cultures what romans involved
in their culture. Those mythologies had their gods too, and their
characteristic influenced the Roman mythology.