Why not just self-host NetBox myself?

You can! It's an excellent open-source project, and plenty of teams self-host happily. The cost of self-hosting shows up later when you have to maintain Postgres and Redis, testing, babysitting, etc.

You can, it’s an excellent open-source project, and plenty of teams self-host happily. The cost shows up later: the Postgres/Redis stack, version upgrades you have to test and babysit, plugin compatibility, backups, and the quiet drip of person-hours that all of it consumes. Palpabl exists for teams who want the NetBox data model but don’t want it to become one more system they’re on the hook to keep running.