Also making a lot money off what is essentially a huge casino. (games that use Addictive Gambling Mechanics to sell Micro-transations)
The thing with games is that the box price is extremely under what consumers value them, so selling consumers small bits of the game as micro transactions is the way games extract their actual market value. It doesn't deliver more value than before, but the current monetization better represents the value it delivers to consumers.
Some whales clearly suffer mental health issues (just from looking at the timing and amount of the transactions). The remainder are almost exclusively money laundering of some sort (usually converting stolen credit cards to game assets that can be sold for real money).