21st Century Classical Greek -- passive redux

Under what circumstances does Thucydides use passives intead of ergatives?

One of our first passives was I 2.6:

καὶ παράδειγμα τόδε τοῦ λόγου οὐκ ἐλάχιστόν ἐστι διὰ τὰς μετοικίας ἐς τὰ ἄλλα μὴ ὁμοίως αὐξηθῆναι:

When a populaton grows, there is no one agent responsible. Also, no one agent was responsible for each of the multiple possible reasons why the population increased.

I 8.1

καὶ τῶν θηκῶν ἀναιρεθεισῶν

The opening of the tombs for cleaning up Delos was done but who did it is irrelevant.

III.85

ὕστερον δὲ οἱ φεύγοντες τῶν Κερκυραίων （διεσώθησαν γὰρ αὐτῶν ἐς πεντακοσίους）

some general bunch fled for their lives, comprising about 500 people.

But then we have I 54.1

οἱ δὲ Κερκυραῖοι τά τε ναυάγια καὶ νεκροὺς ἀνείλοντο τὰ κατὰ σφᾶς ἐξενεχθέντα ὑπό τε τοῦ ῥοῦ καὶ ἀνέμου,

The agent here is inanimate. We can’t put a name to inanimate actors, even if they were the principle movers in what happened. We can’t use a fully transitive form because that would be executive voice and an inanimate agent can’t form intent for doing something. Ergative is likewise unsuitable because of how often it leans toward a deliberate action.

This is different from Biblical Hebrew. BH uses agentless verb forms in narratives when it’s irrelevant or understood who the agent is and in the latter situation it’s usually Gd. As narratives, which rely for their interest on action, BH doesn’t use agentless verb forms often. Neither does Thucydides. Scholars may use them to imply that anybody knows whatever idea they’re pushing – but then if that were true no scholar would need to write it except as a reference to a supporting source. Go back over some of the scholarly books you own and see how often this happens.