Variable Rewards

Unpredictable or random rewards are more addictive than a predictable schedule.

Casinos know that slot machines are more addictive if they pay out a random reward at unpredictable times. If people always won back 80% of their money on each pull of the lever, it wouldn't be an exciting game and wouldn't be addictive. It's the unpredictable and random nature of the rewards that keeps people playing with the hope for that rare big jackpot.

A constant or predictable schedule of rewards is not very exciting. This is why games often randomize the rewards that you receive for finishing a level or defeating an enemy. By making the rewards like a slot machine, they are trying to make the game more additive. They may also be trying to extend gameplay by making you grind longer to get what you want. If you need a certain item, but it only appears as a reward 5% of the time, people will keep playing over and over with the hope of getting that rare item. If the game has limited energy and forces you to wait to play then people may end up paying money to skip the wait.


Examples

Single City: Life Metaverse Single City: Life Metaverse
"gives random extra rewards when doing tasks"

Titan Quest: Legendary Edition Titan Quest: Legendary Edition
"Random loot from bosses encourages grinding for loot"

The Walking Dead: Survivors The Walking Dead: Survivors
"Rewards for daily task and in game progression(no story, just how much you built, collected and killed)"

Life Makeover Life Makeover
"There are small rewards for everything from checking the news page to sharing a screenshot"

Tap Away Tap Away
"SO MANY THEY'RE LIKE WORTH NOTHING LIKE I SAID IT'S ANNOYING AND YOU CAN'T OPT OUT"

Geometry Dash Geometry Dash
"https://geometry-das​h.fandom.com/wiki/Tr​easure_Room#100_Key_​chest"

Melvor Idle: Ad Free Melvor Idle: Ad Free
"Random loot, random pets, random task rewards"

Puzzle Page Puzzle Page
"After completing 15 puzzles, you get a random reward."

Merge Mansion - Mystery Game Merge Mansion - Mystery Game
"You get XP and occasionally other rewards for completing tasks."

The Manga Works The Manga Works
"Some rewards aren't random, namely experience from trying new themes and from winning trophies. However, "Going out" randomly gives you Plot Points (an integral part of the gameplay loop), the player can randomly gain experience when working on a manga, and even training has an element of luck. On occasion, you may get a higher-than-usual stat buff from training your character."