This conspiracy theory doesn't have great explanatory power: the USG has ample legitimate sources of photographs for individual citizens, via licenses, passports, and records collected in the courts. There are no meaningful restrictions on what the USG can do with those photos, because they're not private information.
The USG has also openly applied facial recognition already, for things like border control. They're not really hurting for data sources.
I'm also not defending the government's decision to use ID.me; I'm not happy about it. But I think the reason behind it isn't some shadowy data harvesting plan by the USG; it's probably something between "we didn't want to do the paperwork to authorize, fund, and build this internally" and "someone's nephew works at ID.me."
The USG has also openly applied facial recognition already, for things like border control. They're not really hurting for data sources.