After a while people would grow wise of this tactic and start redialing after waiting for some time. We could build a whole lot of efficient and beautiful systems, if only not for the people...
Exactly. I've never had the time to dig into it, but these LIFO-optimality results always strike me as being non-physical or introducing some implicit hard-to-model effects.[1]
Like you say, people can just re-enter the queue, or (in meatspace) form a meta-queue that vies for entering the moment it has an open slot, reproducing FIFO all over again.
Furthermore, you get a lot of pro-cooperation effects (necessary for queues to work at all) by giving people "skin in the game" in the form of valuing their place in line. Once people lose nothing by inventing a new name and re-entering the line, that's all gone, and they no longer have an incentive not to be disruptive, which throws off disproportionate negative utility onto the rest of the system.
What's wrong with degrading from LIFO to a random queue due to client retry, when you're starting from a FIFO that is already failing client expectations?
Nothing, if it's just used for that (narrow, least-bad, degraded) situation. I was addressing the more general point that LIFO queues have some actionable superiority over FIFO in the general case because of the theoretical results cited in the literature.
What's the problem with this? redialing essentially converts the FIFO/LIFO queue to a random queue, which isn't particularly worse.
Ultimately, the utility of "lower 50%ile" vs "lower 99.9%ile" is a subjective choice.
The value in LIFO is the observation that real people would rather their 10-minute request fail and require a retry due to LIFO (since they are already disatisfied with the original service*) than their 1second request take 1 minute due to FIFO.
People feel cheated when you request them to wait, but they can get better outcomes by redialing. It violates the trust between the call center and the dialer. Leaving people to wait forever is a bad, bad, bad move.
Alternative scenario: Someone figures out the best way of dealing with LIFO is spamming requests until one gets through and you end up with several multitudes of queuing work.
Like you say, people can just re-enter the queue, or (in meatspace) form a meta-queue that vies for entering the moment it has an open slot, reproducing FIFO all over again.
Furthermore, you get a lot of pro-cooperation effects (necessary for queues to work at all) by giving people "skin in the game" in the form of valuing their place in line. Once people lose nothing by inventing a new name and re-entering the line, that's all gone, and they no longer have an incentive not to be disruptive, which throws off disproportionate negative utility onto the rest of the system.
One day, I promise, I will unpack this result.
[1] My comment from 2015 expressing similar reservations: https://news.ycombinator.com/item?id=10182781