Login.gov had/has some technical gaps for agency customer identity use cases, which is why you don’t see it used by some agencies yet (depending on their customer identity assurance requirements). The outstanding technical gaps will be closed eventually, at which point id.me can be phased out as a private for profit idp vendor.
https://legis1.com/news/logingov-technical-issues-gsas-platf...
> GSA has closed most of the gaps GAO identified in 2024 and 2025, but the remaining recommendation has a direct operational consequence. GSA has developed a public roadmap and created a Partner Advisory Group, but GAO says those steps do not demonstrate that the specific technical challenges agencies identified have been resolved or that mutually agreed-upon time frames have been established.
> GAO will continue monitoring GSA's progress. Until those time frames are established, the federal government's government-wide identity verification service retains an unresolved implementation gap as fraud and identity-theft threats continue to evolve.