Let me guess you ended up on United thru Chicago. NCL has a major deal with them. Cruise air is always a gamble.
Original routing for my son was Tampa to Chicago to London. A couple of emails and calls and he ended up Tampa Miami London.
The few times I booked NCL air I have been lucky. Non stop Newark to London on Virgin.
My favorite NCL air my partner at the time was coming from Buffalo. They routed her thru Clevland to MIA. The sent me to FLL. On our return she went FLL to Buffalo and I was out of MIA
The goood news in all cases I made the cruise and had a great time.