Looking at subject of closing an interline agreement: My cynical guess is that someone has worked out that they are not getting the financial benefit of the balance. They have calculated that they do more of something than another, or that it costs them more to administer or something.
The end result is to show that, by cutting this out they can save $$$ per annum. They will consider saving that across (say) three years to be worth any possible bad customer reaction.
Also, with this kind of subtle change, the fall out will not be seen for a long time and, largely unquantifiable. That for the simple reason that they will no longer be doing this activity so they don't have to count it and just count the 'savings'.
I could go on but I think you know the story ...