So, when a UA employee flies AA because of the price, that really shows that price is the number one factor.
In the days of regulation, people picked airlines because of a variety of factors. My father avoided Eastern like the plague, because so many flights were late. He liked Delta morning flights, because its breakfast were southern, often with grits. When his salary grade permitted him to fly F, he flew Braniff whenever possible, because dinner often meant cherries jubilee for dessert.
These days, about the only time people choose based on the soft and hard product are for flights to Europe, Asia, or Latin America, if you can fly J or F.
And they plan to deploy the plane to Latin America. For all the people who say this is because people are choosing the lowest prices, does that also apply to business class passengers to Latam/Caribbean destinations like UIO, LIM, POS and BOG? The business class pitch has also been reduced on this plane and as stated before, there is no dedicated business cabin; just a curtain basically between main cabin and business. Are the business class passengers also looking to pay Spirit fares and only deciding based on price? Main Cabin Extra also has reduced pitch. Are the elites and non-elites who pay extra who reserve the MCE seats also bargain basement discount hunters?
You need to factor into the discussion the issue of corporate contracts. A person may upgrade to MCE, but his company may be paying for him to fly Y on AA, and he can't fly WN, B6, UA, DL, and AS. By the same token, how many people upgrade to F?
Back in the 1970s, my father worked for Swift & Co. Anyone who was a director or higher could book F. If a director was traveling with employees who were lower than a director, they could also book F. But even in the early 1980s, the rule changed, and directors or vice presidents traveling with managers had to fly Y. You saw a lot of directors deciding they needed to travel early or later, so that they didn't have to fly Y with direct reports.
Fast forward to today. I know vice presidents of large companies who can only book domestic Y. Companies aren't as generous with premium travel as they were. My wife used to work for a company that used to allow travel in F for domestic flights over 4 hours. That was back in the early 1990s. By the time she left in 2005, there was no F travel in the system, and someone in Chicago flying to London would have had to book Y, because there was a minimum of 10 hours scheduled flight time, in order to book J.
For my wife to fly with her current employer, it takes her boss and his boss to sign off on travel. Needless to say, she isn't the road warrior that she was with past employers, because travel is frankly frowned upon for anyone who isn't in a senior position with the company.
If seats in F tend to be filled with upgraded passengers, then airlines may very well decide that the F cabin on a narrowbody doesn't have to be that nice.
The funny thing is that my father-in-law used to fly Delta a lot in the 1990s, when he consulted part time while teaching college full time. He flew enough that he was second tier on SkyMiles. But, even between 1994 and 2005, when he stopped traveling for business, he had a lot of complaints about how DL domestic F had gone downhill, in terms of the soft product. So, should we really be surprised that AA is scrimping on the MCE section of Y and the F cabin?
Whereas in the 1990s, a lot of people flew for business at the drop of a hat, today the old WWII line, "Is this trip really necessary?" seems to be used a lot.