You’re actually wrong about that. It’s not just the big shiny reward messages. It’s also the ‘Why’ it happens and ‘How’ it happens.
Such as if you just click a button, and each and every single time you click a button, you get the reward, it won’t work. It becomes predictable. You know what happens when you click the button. It stops becoming a reward, and instead a chore, and boring task.
Instead, randomization of Reward, is what clicks the longest. Because you can’t predict it, you can’t know when it happens, where, or why. This is why Slot Machines, Lootboxes, and Random Drops from enemies are so addicting. Because even if you ‘Lose’ 99 times, or even just 1 time, the instant you get the ‘Jackpot’ reward, your happiness skyrockets through the roof.
This is a great video about it, and how video game devs try to trick people to become addicting to their games. Which explains it, and points to another video that also talks about it.