Originally Posted by
Ryanardo_daVinci
I understand the rule, but I don’t understand why it exists. Does anyone know?
The US doesn't want foreign airlines undercutting US airlines on domestic air travel markets. It is purported to be a national security issue to ensure that there is a fleet of aircraft under US control. Similar rules apply to passenger and cargo ships (Jones Act).
To be clear, the government is not going to penalize you if you somehow put together a cabotage itinerary. The airline would be penalized for carrying you.
Here is the government's official view on exemptions - they are only for emergency situations when no US carriers are available in certain markets.