Identity providers became quite standard these days. Why would a company care about another solution for Single Sign-On (SSO) if they are already using an identity provider? The answer is multifold.
Compatibility
Firstly, it's important to note that not everything is SSO compatible.
Consequently, there are often weak links in the infrastructure if everything isn't put behind the strong authentication of an SSO provider. These weak links often present as static key-based usernames and passwords spread across the infrastructure. Primarily when there is insufficient time to build an SSO connector.
Implementing OpenID Connect or SAML protocols for tools that do not inherently support them is tricky.
Intermediary Solution
A set of tools that are difficult to add SSO support to are open-source databases.
The connectors are not ideal. If you're running on a cloud provider, you may have the option to proxy connections through SSO, but even so, you're essentially provisioning temporary database users. For a period of time, you're exposed to the legacy database authentication methods. Such systems are primarily provisioning tools for credentials. They're a step up from static credentials.
But still fall short of the authentication power offered by native SAML or OpenID authentication.
