The main reason for me was RBAC. Converting db-to-api is not that hard but providing access control almost always requires some form of middlewares. Hasura does RBAC very well.
Another feature that I haven't deployed but find useful is webhooks. You can trigger webhooks as your data changes.
I do need a server to handle object storage, email and cron so it's not a 100% there, but I can see the appeal of rapid APIs at low cost.
Also subscriptions are <3.
All the best to the Hasura team.