I've heard Blizzard does the same thing for valuable random drops (like legendary drops in Hearthstone and Diablo 3): instead of being random, there's a proc rate so you can't get screwed by chance.
They do it in Hearthstone for pack openings, the players call it the "pity timer" - you're guaranteed to get a legendary card after opening 40 packs or something like that.
There are even websites like https://pitytracker.com/ that keep track of where you are in your chances.
There are even websites like https://pitytracker.com/ that keep track of where you are in your chances.