This is one of those things about rules light games that kinda grates on me. They don't have mechanical support for long-term play, that's true. But that doesn't mean they're limited to one-shots or short campaigns. Most of the advancement in rules light games can easily be handled diegetically, that is with in-fiction rewards and advancement. Things like titles, resources, allies, contacts, land, castles, ships, soldiers, mines, fictional positioning, etc. It's all still up for grabs. These games only lack extra +1s to throw at PCs to show "progress"...while pretending that the math on the monsters' side doesn't also improve.