If they already know, why all the fuss about ID enforcement?

The government is largely incompetent about proactively sifting through vast amounts of information for relevant bits.

That’s minimal defense, but it’s worth remembering the difference between what it in theory knows and what its actually paying attention to.

If they already know everything, why is there always a push toward adding friction to the process they already know everything about?

There is a difference between the NSA knowing and being every petty burocrat being a trivial administrative subpoena away from everything.