[thejeff]

A common debate. The simple answer is that it's a game. It's supposed to be fun. People stop playing when it stops being fun. Some will stick it out longer than others in the hopes that it will start being fun again or because they feel an obligation to help keep it fun for others.
People also find different parts of the game fun. Pretty much everyone enjoys winning against a good challenge. Many also enjoy putting up a good challenge while losing. Few enjoy getting slaughtered. Some only enjoy winning, but I suspect they're mostly new players, since they can't win all the time in MP and will likely give up playing.

Personally, I find much of the late game micromanagement tedious at the best of times. If I have to put an hour or more of work into each turn without any real hope of victory, it gets very old very fast. If I'm actually being killed fast enough, I'll probably play it out until at least near the end, but I'm not willing to play out a losing war for months on end.

Due to the way 4X games tend to work, it's very hard to come back if you've fallen too far behind in resources or research. If you're in late midgame when your opponent has dozens of Tartarians and is Wishing for Seraphs, you really aren't going to make much of a difference in the game. Even if he isn't bothering to squash you quickly because he has other enemies.

I agree that people who quit after losing the first major battle are frustrating. But there's a big difference between that and playing to the bitter end no matter what. The problem is that, from what I've seen, often that losing series of battles isn't very interesting. It's having your gem/gold income drop drastically as Ghost Riders hit 4-5 provinces a turn, while you sacrifice everything you've got to stop one of several armies and each turn more uber SCs join the battle. But it's still going to take a dozen turns or so to actually die. Which at late game pace is going to be a month or so.

If you're going to start a game with this kind of commitment, I strongly suggest reasonable victory conditions. It seems to me very rare that a game actually comes down to the last two players. Either victory conditions are met while there are still more players or the outcome is clear enough to all that they concede.

Is a master chess player who sees mate coming 5-6 moves out and concedes a quitter, or does he just have the grace to acknowledge the inevitable?