Sancho Panza wrote:

Why does the US federal gov't have an interest in whether or not
you are bringing or leaving the country with more than $10k any
more than a state gov't would want to know the same thing?

Gee, d'ya think money laundering might be a concern?

Transporting cash (or cash equivalent) between places is not money
laundering.

There are already reporting rules on the bank pertaining to
depositing large sums (coincidentally $10k) into any US bank.

Which is irrelevant, because the cash sums that exceed $10,000
can be easily broken down into unreportable sums.

And the same goes for transporting cash.

If the gov't believes that you are in possession of the proceeds
of crime, then the onus is on them to investigate, arrest and
charge you - AND YOU HAVE THE RIGHT TO REMAIN SILENT. Why is
that right somehow magically erased at the airport?

The right to remain silent is not erased. Just your "right" to fly.

Your flying is done and finished by the time you walk up to a CBP
agent. That agent does not act as any sort of gate-keeper who gets
between you and the plane.