I often find myself wanting answers to questions that require linking data, and I also want to codify those links somehow, so a single-file, row-oriented database seemed like the appropriate way to get that.

You might actually be able to get away with less structure and just dumps thoughts and ideas, statuses, and documents into $AI and have it generate ad-hoc reports.

In which case, a text file might be the right interface.

Kind of a non-answer, I realize.

I suppose the answer is: because I had a relatively specific idea of what I wanted to build and I didn't consider not building it.