Perhaps a dumb question, but how do you get data into it if you’re not doing writes

I think it's just immutable once you've generated it. No need to update indexes or check consistency on writes, no need for transactions, etc.

Generate it one time from a source tsv file or folder of media.

Think historical records of, say, share values for past years. You might have a single db for 1900-2000, for instance. Things like that.

Not everything needs to be real-time updated.