Keep in mind that what you listed aren't explicit Cleric subclasses but rather areas of influence for the deities. The People and Cultures section is listing well, common cultural aspects of the more prominent groups in the setting. They don't grant spells because, in the context of the setting, they don't exist. But their lack of existence doesn't necessarily ignoring their entry, for Roman influence on Jewish and early Christian history cannot be underestimated, and it would be an oversight to not discuss how their religious practices clashed with the Abrahamic faiths.
I can understand your confusion as such an entry in other settings would more or less be an indication of "here's some ideas of appropriate Cleric subclasses for these gods." Instead, think of it more as "religion is an important aspect in this Biblical Fantasy setting, so here's a brief listing of the religious traditions of pagan faiths as a contrast."
