Because elite customers are generally more profitable overall, and to incentivize them to stay is much cheaper than letting all of those potential spend dollars flow to a competitor? How do you know how much United is selling those seats for? Those full F cabins could be mostly mileage tickets or mileage upgrades, or buy-ups offered cheap, no one here has any possible way of knowing. Of course if Kirby actually wants to thin the elite ranks and slash the number of elite members at the higher levels by a significant amount, then sure, they can choose not to offer anything - unless of course a competitor makes an offer because we all know United management is completely incapable of thinking or innovating for itself.

You're using two false metrics to posit that United should not extend membership another year - one, your personal observation of full cabins which does not translate to actually making money even when this fact is pointed out to you multiple times, and second, an apparent desire to see all of the "losers" who didn't fly as much as you did personally, get thrown off the bus.