Another couple practical issues - besides all the practical issues already raised - are the fairness and predictability aspects. They are working with emotionless "agents". People in real life are anything but emotionless and fairness and predictability are a good chunk of what holds society together.
If you get in a FIFO line, you can expect to spend as much time there as anybody else in that line. Maybe it's an hour. Maybe it's ten hours. But whatever it is, nobody is getting any special breaks. You wait it out with the people next to you for as long as it takes; you're a little group together. FILO doesn't work like that; you might be stuck in that line for hours and watch dozens of neighbors come and go with only a few minutes wait. That's infuriatingly unfair and encourages resentment against whoever's behind you.
Which brings us to predictability. Anyone can look at a long, slow moving FIFO line and guess at how long they might spend in it and make a choice on whether it's worth the wait. Nobody can do that with a FILO line. You might hop on the back and immediately be taken care of. Or you might get sandwiched and become part of the damned front, forced to watch with envious, burning eyes at those lucky backfolk who come and go all day at will.
And, of course, it's easy to cheat. Suppose that you're stuck in the front. It'd be simple to leave and come back in a few minutes. Nobody's forcing you to stay there, right? Cheating is harder in a FIFO line where the only forward motion permitted is the slow locksetp and would-be queue-jumpers can be spotted instantly.
In short, it may theoretically be a better system, but it's not a human system and humans are generally the ones doing the queuing.