Why do long-term campaigns matter? Simple - for the story of the campaign and the players in it to develop and unfold. If "the story" emerges from the play of the game, it's not unreasonable to want to see the "domain game" emerge from character development. (Not too surprisingly, games like Adventurer, Conqueror, King are aimed at making that possible.)
Recently, I had this realization presented to me by one of my players. After I told him about my new campaign setting, Aldwyr, Dave looked at me and said, "Well, I like the sound of that, but I hope there's room for some real character development" ...by which he meant opportunities for play in the higher levels of the game - really anything over 7th level, as we hadn't gotten there in about 18 months of play in the campaign I had been running. Combined with some thinking about pacing, and I decided to go back and do some background reading. I ran across this quote from Gary in the last issue of The Strategic Review, April 1976:
...which reveals a few interesting points about how Gary saw higher level play:It is reasonable to calculate that if a fair player takes part in 50 to 75 games in the course of a year he should acquire sufficient experience points to make him about 9th to 11th level, assuming that he manages to survive all that play. The acquisition of successively higher levels will be proportionate to enhanced power and the number of experience points necessary to attain them, so another year of play will by no means mean a doubling of levels but rather the addition of perhaps two or three levels. Using this gauge, it should take four or five years to see 20th level. ("D&D is Only as Good as the DM")
- Game play should happen regularly and consistently. Consider: "...50 to 75 games in the course of the year...."
- Advancement to "name level" is never guaranteed: "...assuming that he manages to survive all that play."
- The rate of progress to higher levels slows considerably.
- A long-term campaign is one that lasts easily more than a year, or even two.
All of which suggests a tension in the modern era between developing a campaign with that kind of timespan, and all the games we'd like to play, and the limited amount of time anyone has. But if you want to maintain player interest, you need to think about they might develop their character - as long as those characters survive.
I don't think of this as a bug, more of a design feature. But it is something that can come back to challenge a referee as they go from "town, nearby dungeon, and low-level player-characters" to something much larger and more developed over time. I'm rather curious to see where this will lead.