Unpredictable or random rewards are more addictive than a predictable schedule.
"When you complete a daily mission, you can see the possible pool of loot, but it is randomized within it."
"There are in-game chests that give a inconsistent number of specific valuable resources."
"The game will help you out a lot and making you feel good then the next time you have to pay to get that same reward"
"item drops on levels are never guaranteed, requiring players to waste stamina on grinding"
"there are spots on the level map that give you a random reward when reached, and completing the daily puzzle gives you a random prize"
"there are a few types of seeds (particularly event seeds) that give you a random pikmin when it finishes growing, so it's impossible to determine when or if you'll be able to finish an event with limited time pikmin"
"So. Many. Rewards. And there's mostly just random and end up being useless. I cannot stress this enough."
"Minigames can be played to unlock random clothing items. These minigames are optional."