I’ve had this experience many times over the years. But...
Let me paint you a picture: one which will likely be horribly familiar for most of you. You’re playing a game - a long game, but a good one. The first two or three hours were utterly fantastic and had everyone buzzing, focused on the table, totally immersed in the experience. The hour after that it became pretty clear who was going to win so, even though the mechanics of the game allowed for someone to come from behind to take the win, everyone eased off a little bit. But it went on: for one reason or another, the lead player just could quite make the leap to the finish line and another hour dragged by before it ended, an hour where everyone was pretty much bored and fed up because they felt the game was a foregone conclusion. The group sits back and, in post game discussion, they all agree the game actually ended a good hour, maybe even two, before the victory conditions were achieved. Which begs the question of why, if it was so clear cut, did everyone keep on playing once the game ceased to be fun?