If you use Customs and Border Patrol's trusted traveler programs (or some other gov sites), you may already have a login.gov account since that is what they have been using for a few years now.
Yet the reason I have a login.gov account is for my NEXUS enrollment which means I've been fingerprinted, background checked, had my passport number linked, and been interviewed in person by two different governments. That seems pretty identity verified to me.
If I have to go through some other step, especially if it involves yet another biometric or interview check, that's going to be annoying.
The only thing you have to do to enroll in login.gov is verify your email address.
And optional feature of login.gov is to verify your identity further by uploading a photo of a state ID, and entering your SSN and phone number. When you validated your identity in person with CBP, this was not that.
This isn't snarking at you directly, just all I'm really hearing is that the government will happily mix whatever it knows about me for its own purposes but when it comes to making things easier for me (wherein they've literally seen me in person and looked over a stack of my identifying documents), no way that's "violating my privacy."
If we are going to have an all-seeing panopticon can't it at least be convenient?
Maybe it's a coincidence but it seems like the two agencies work together. They also apparently withhold government services if they think you owe them money. Not sure if I think that's amazing, or petty. Leaning towards amazing though.
I believe that although you are validated to a higher level with a trusted traveller program, they cannot or have not been able to share that validation with IRS directly.