Something else I’m thinking about: the assumption that the cultural institutions of the ancients were ageless and unchanging.

They weren’t.

For instance, when did the Athenians stop celebrating Anthesteria?

If memory serves, Plutarch is one of the last authors to speak of carrying out the rites; subsequently references to it tend to be in the past tense.

His observances are also very different from the evidence we have for the Classical Athenian form of the festival, which differs again from what was done in Southern Italy, and likely Ephesos and Magnesia too.

Interesting fact: Themistokles (of 300: Rise of an Empire fame) is credited with transplanting Anthesteria to the latter polis, where he was banished after successfully defending his mother-city from Persian incursion.

I bet Orestes’ Supper held some interesting resonances for him, especially considering the tragic hero’s ties to the Black Sea region.