I would not self host a password manager, simply because I don't want running something like that on a 24/7 online server.

Still, if I needed to run a password manager on a server, I would rather self host it than use a hosted service from someone else.

In my opinion, running such a service commercially is a much harder problem than self hosting it and has a much bigger attack surface.

This is IMHO what many people do not understand about hosting as a service vs. self hosting: The full time DevOps/Admins etc. people who work at the hosting service are hopefully better than me at hosting stuff. At the same time the problem they have to solve is so much harder than self hosting, that even if they are 10x as good as me, running my own little service with a firewall, rate limiting and monitoring should at least not be less secure.