They pioneered the "battle pass" model for cosmetic items, and their constant release of skins, dances, etc can create a lot of recurring revenue I imagine.
Yup, I think they definitely found the sweet spot for making revenue from games — offering players sweet returns if they keep playing (you buy the battle pass for 1000 vbucks, but you can earn back 1500 just from playing casually) while still keeping it relatively competitive and not "pay to win". They did host a $30 million world cup event after all :)
Edit: Insert joke about Quantitative Easing here