I think the nub of his argument is that "Flying Spirit instead of United would set you back on these reward goals, so you decide to pay a higher ticket price, or fly at a less convenient time, just to remain in United's network." Maybe for some people it was to accumulate miles, but I tend to think that the main goal of the frequent flyer is usually to make their business travel less of a hassle. Miles are only useful to the extent that they do that. And the main feature that did that was an upgrade. If UA or another airline could offer me an upgrade for miles at booking, I might get that ticket even if a little less convenient or a little more money (though even there, within limits). Since it has become more difficult to upgrade at booking, loyalty has waned.