Why is the use of standards so important in IAM?

Because a relying party or broker that connects to several identity providers would otherwise have to handle a different identity format and protocol for each one; common standards for protocols and attributes keep the integration cost constant instead of growing with every new partner and make heterogeneous federations possible at all.

* Without standards the integration cost grows with every IdP; with standards it stays constant. *

The RP-centred model makes the problem visible: with four IdPs that each represent identities differently and speak their own protocol, the RP needs four integrations, four attribute mappings and four sets of test cases. Standards such as SAML, OpenID Connect and SCIM, together with agreed attribute vocabularies, turn that into one integration that any compliant partner can plug into.

Standards also underpin the trust side: metadata formats let participants publish endpoints and keys in a machine-readable way, and assurance-level frameworks let an RP interpret "this user was authenticated with two factors" the same way regardless of which IdP said it. Without standards, brokers would have to translate everything, and full-mesh federations would collapse under their own integration effort.