1. Built-in audit trails. Git's a hash tree, right? So you can't tamper with it? Wrong. You can force push and delete commits. By default, git garbage collects dangling commits and old branches. In order to make a cryptographic audit trail, you'd need to publish the hash tree publicly and non-deniably so your auditor can know if you tampered with the logs.
2. Atomic transactions. Many databases support these, with a lot of granular control over the details. Postgres is one of them. (The ones that don't may have good reasons.) Git does not have much granular control; merges are not guaranteed to keep any data intact.
3. Distributed architecture. Good point. But wait, that's not really true. How do we decide what the real "main" is? It's whatever main is on your upstream, which in almost all cases is a centralized server. And if it's not, git doesn't provide any automated tooling for dealing with conflicts between multiple sources of truth (no algorithm for byzantine generals, for example). So this is a red herring.
4. Content addressing. Does this mean a commit hash? Like, say, an _index_ but without the ability to index over any other data?
In my career, I have seen git used twice as a "database" in a sensible way: for tracking source code changes (that is, changes to structured text files). This is precisely the use case it was designed for. And in both cases, it was actually underutilized---no real merge capability, just file versioning, so they could have gone simpler.
But git is not even good for most "collaborative text editing" since merge handling is not automatic. You wouldn't use it for a google-docs style platform, for example.
Edit: formatting