it's also super hard to build a great f2p and i think CSGO easily is the best. they bootstrapped it for almost 2 decades from a mod made by Minh Le to what it is today and I must say it is the only f2p game I regularly play.
simply because it actually pays to play. I've made about $20 bucks this month from just selling cases given out randomly at the end of each match. It cost me nothing to buy yet the in game items (cosmetic skins that don't influence gameplay) regularly sell for good money.
it also make sense to buy the keys to unlock the cases sometimes simply because you might unlock a skin that fetches far more money. so it is a bit like gambling in that aspect.
i'm just constantly amazed how they were able to pull the economics behind this. clearly the ppl who expect a 10~100x ROI on their keys must outnumber those selling the cases. I mean I can imagine a bunch of people just farming cases day and night. Perhaps even a sophisticated AI could pull it off since the in game drops aren't even correlated with your performance.
even more impressive is how this is all legal since it really is gambling of sorts.