A quick remark relevant to this thread. When UA ran NRT<>BKK with a widebody (sometimes 744, sometimes 772) a decade ago, I was good friends with a senior staff member of the agency that managed UA's business in BKK (not a UA employee, but he had a UA contractor's badge). He was a direct participant in the conversation when HQ told his agency that service would be discontinued. The route was profitable, but HQ determined that UA could make more money by deploying the aircraft (it took one dedicated plane) to another market, along with the crews (pilots would fly US to NRT, layover, then to BKK); FAs were non-union BKK residents that only flew that sector. He explained that UA made most of its money on O-D Japanese travelers; they filled the rest of the seats with mostly leisure travelers connecting from the US. Many of the J pax were upgraders using GPUs or mileage. Establishing the codeshare arrangement with NH made more financial and operational sense.

At the time, UA had no plane that could fly US-BKK non-stop. Now, with the 787-9, it can.