I can understand that when it takes a few minutes at most before—if not the reward you’re looking for—at least some kind of reinforcement stimulus (e.g., with a slot machine, seeing two of the three wheels line up, making you feel like you “almost got it.”) That seems “fun”, if just due to a bug in human brain-hardware that you should probably not want-to-want.

But these games don’t work like this. When you’re trying to find a rare drop, there’s nothing giving you the feeling that you’re getting any “closer” to it. You just have to throw days of blind dice rolls for no reward at the game, before it’ll turn around and give you the reward once. Variable-schedule rewards shouldn’t actually work at that sparse a frequency. People who get easily addicted to things don’t usually find themselves grinding for rare drops.

The people who do do this kind of grinding are people with big reserves of determination. And I don’t really get what they get out of it.

It builds up. Early in the game you get useful drops very quickly, and slowly slowly over time the frequency goes down until you grind for weeks just waiting for that single drop.

One incentive is that you get other more common drops along the way which help beef up your arsenal and help you progress at faster and faster rates.