I like the idea of "Fronts" from PbtA; keep things progressing when the PCs don't pay attention to them.
A videogame and not really an RPG in the conventional sense, but
Kenshi manages to create an amazing party-based sandbox full of great adventures with the simple hunger mechanic. The game world is a desert with no naturally growing edible plants, and pretty much all animals are evolved to defend themselves against the many huge predators, which makes them really dangerous to hunt. Because the hunger bar of the characters in the party is constantly going down, you are permanently forced to ensure a steady supply of food. You just can not sit on your butt and let time pass, you have to be active to keep food coming in. You need to mine resources to trade for food, train and equip your characters to be able to hunt for food, or build a base to grow your food. The first option is very slow and gets boring quickly, and the last option means you're setting up a giant beacon for all the raiders in the surrounding desert because they also need your food. And you can have absolutely amazing adventures exploring the desert to search for new resources that allow you to improve your food production or strengthen your defenses in your base or better equip your characters to fight off raiders and predators. Entirely with basically just random encounters and no meaningful dialogs, and no kinds of quests of any kind. Trying to find a way through a pass occupied by bandits to avoid a giant detour through monster territory. Trying to get your severely injured and bleeding characters carried to a village where they can recover before the beasts of the desert catch the last ones that can still walk. Trying to retake your base after you've been thrown out by bandits. Sending a rescue team to get captured allies out of prison cages in a hostile town, or race from your base through the desert with a backpack full of bandages to save your bleeding and unconscious friends who were away to deliver your goods to the market.
The really important lesson I've taken from this game is that default actions and incentives come in both the form of pull and push factors. Typically in a dungeon crawling sandbox campaign, we are dealing with the search for treasure and XP as pull factors. There are things out in the wilderness that are desirable to reach if the players can get past the obstacles, but the players don't have to pursue a specific source and can instead choose to go after another source where the risks don't seem as high compared to the rewards.
But push factors can be just as powerful, and even feel much more appropriate and interesting for some campaign premises. The hunger mechanic of Kenshi mentioned above is one such push. Water requirements in Dark Sun are another one. When you're only dealing with pull factors such as rewards waiting for those who overcome the obstacles standing in the way, there's always an option for players to decline and instead keep looking for other opportunities that seem more promising with better rewards for the involved risks, or which just seem more thematically and narratively appropriate for the personalities of their characters. This can lead to the situation where the players don't really want to pursue any of the options known to them and the game drags on as they wait for new opportunities to present themselves. That's the very important difference with push factors. When you motivate players with push factors, then they are on a clock. Water is running out. Food is running. If the PCs don't get off their asses and do
something, they will die! Don't like any of the options presented to you? Tough luck. You're now forced to pursue something that doesn't seem that great to you simply to buy yourself more time to find an interesting pull to grab on to. And just because the characters don't like the activity they are doing doesn't mean the activity isn't fun to play for the players. That's where drama and desperation comes from. Being forced to do things that are unpleasant because you're being forced to by circumstances outside your control.
This is one of the reason why many space exploration games have the ships of the PCs come with regular maintenance cost, and frequently have the party start out with a large debt to some dangerous people. Any time the players find a job opportunity for their party and decline, have the clock tick forward increase the push by one increment.