Most games allow you to progress by actually playing the game. You can step away for 5 minutes or 5 years, either way everything will be exactly as you left it when you come back.
Idle games expect you to leave and will continue to progress without your direct involvement. The whole concept is to start out with minimal resources (like a lemonade stand) and slowly accrue more and more resources and upgrades until you've reached the maximum (like a michelin star restaurant).
Blockchain tech is well suited to this time-based mechanism. Because blocks are applied to the chain at regular intervals, the clock is baked into the infrastructure. You transact to purchase upgrades and your rewards can be calculated without any further transactions.
This kind of game doesn't need blockchain to work, but it does open up some interesting design space. These types of games are pretty much exclusively single player. Players don't interact with each other except maybe to compare high scores. But imagine if the upgrades themselves were NFTs with increasing scarcity at higher levels. The game would be a race to see which player reached the top first. Or perhaps your upgrades can only be gained by making deals with other players. There's a lot of interesting and untested ideas to play with here.
P.S. a lot of blockchain games are play to earn where you get direct rewards whenever you take actions, but you don't see many where the rewards accrue automatically with time.