Federated systems are something that lots of people seem to want, yet they’re really difficult to build in practice. One problem is that it’s likely that participants have a misaligned set of incentives
Identities Evolve - Why federated identity is easier said than done nicely articulates some of the problems, and highlights where things have gone awry before.
This paper is 9 years old, so I suspect there are more up-to-date write-ups. I should probably go and look for some!