Originally Posted by
donotblink
Except it doesn't work that way. M&A has consolidated a vast majority of the airlines, and many routes are only served by one airline.
It's not routinely true that major (or even middling) demand domestic routes have only one carrier. High demand city pairs will often have four, five or even six carriers. As for just one carrier on a route like Chicago-Bangor, well, there are connections.