[foobarian]

I am aware of the basics but it's hard to find details on "why not Postgres" or other standard solution for basically event sourcing.

[diggan]

Event sourcing is usually something you'd have to implement yourself, it's "just" a pattern.

While Datomic et al gives you a bunch of useful features out-of-the-box.

Yes, you can build a query system that allows you to see data at specific points of time with event sourcing, but you likely have to implement that yourself. Compared to temporal databases where it's just (usually) a parameter you pass together with your query.