Obsidian is flexible enough to work as almost anything, including a database. But officially, it’s marketed as a second brain/knowledge base system which is typically geared towards atomic notes.
If you look at the discussions on this forum, the amount of people who use Obsidian for longform writing constitutes a small percentage of the user base. I think the defaults of the theme should cater to the average user, not to the outlier.
But as I said, it’s a customizable setting, so it was more of an offhand comment