> Why would the length of the campaign deter you from playing it?
"Campaign", in this case, doesn't mean something like Gloomhaven's scenario-driven design, with a single character pad and a couple card decks that need to stay in order between serial 1-4 hour play sessions. It's a single game, with huge maps and logistical tables whose state needs to be tracked for the entire duration.
> Isn't it great if you know you have enough content to play the game for the next 20 years?
"Content" in games is generally awful and the modern focus on it is destroying what makes games interesting. Most games, especially competitive games, should become more interesting with repeat plays as you explore the systems involved. Gloomhaven works because the story "content" is largely divorced from the mechanics/dynamics of the scenario so you're playing "the game" dozens of times, and those systems are interesting. Modern narrative campaign games that don't have anything interesting going on in a much smaller inner loop are trash.