You clearly didn’t understand what the Gambler’s Fallacy is about.
It’s also known as the Monte Carlo Fallacy due to a casino there where the roulette wheel came up the same colour something like 17 or 18 times in a row so gamblers were placing fortunes on the other colour because they though the wheel was “due” to be the other colour, not understanding that each spin of the wheel has no influence over subsequent spins.
Each time you create a game, you have a 2% chance of getting the conditions that will result in you getting the gemstone, i.e. right dungeon (50%), mob is present (80%), mob drops the item (5%), but you do realise that the cumulative chance of multiple runs not having the item reduces the more runs you do.
It’s very simple. Do you have a coin? Toss the coin. The chance it came up heads is 50%. Now toss the coin 10 times. The chances that it came up heads 10 times in a row is obviously a lot less than 50%, right?