Chuck beat me to the answer about long campaigns. I have played in, run, and been a part of a lot of them using ICRPG.
And to parrot Nimlouth:
ICRPG, as designed, is actually waaaay better for long campaigns because it keeps the numbers small. Unlike 5e, where you’re a god at level 5 with five attacks, 80+ hit points, and a host of abilities, ICRPG doesn’t suffer that scaling bloat. Consequently, DMs don’t have to work as hard over the long haul to challenge players.
Beyond that, with a loot-based leveling system, each character has at least six ready milestones and over 300 loot options, not counting spells, the ability to choose milestones from other classes, or any of the expansions: Worlds, Magic, Blood & Snow, Vigilante City, or Altered State. With Worlds in particular, there are an additional 100 potential loot options along the Tier Paths, plus all of the Ghost Mountain spells and loot. OMG. There are literally a thousand options to keep progression going for a long, long time.
So, not only is ICRPG designed for the long haul, it’s waaaaaay better than most games and especially well-suited for long campaigns.
I’m not sure a system of mechanics needs to teach you how to run a long campaign. If the rules are silent on that point, there are plenty of resources that can teach you how to be a better DM. No set of rules can do that part for you. And just because there aren’t a ton of reports doesn’t mean ICRPG campaigns aren’t happening. I think as this thread shows, they are happening.
Finally, this topic somehow suggests a long campaign is “better” than a short one. To that I would say, I’d rather watch an episode of Mando than some of the 3 hour Star Wars movies. Indeed, an 8 episode arc might be all you need to tell a ridiculously good story.