There's a really good vox video on why the Concord failed:
This is why it only ever flew transatlantic. It was originally envisioned to also fly across the US, e.g. NYC to LA, but this was banned due to noise concerns.
Had the Concord been permitted to fly over the continental US, it could have been much more successful than it was.
How much that was because of the sonic boom is a matter of some debate.
No, it's actually not a matter of debate at all. See FAR 91.817 [0]
No person may operate a civil aircraft in the United States at a true flight Mach number greater than 1