For example, something that is too complex for your comfort level, a security concern, or maybe your hardware can’t keep up with the service’s needs?
I think that’s what’s kept me at KeePass rather than moving to something like Bitwarden. Since it’s file-level encryption, anything that can serve files can also serve my KeePass database. When I upgrade servers or change to different services, restoring my database is as simple as throwing the file into that new service and going on with my life.