One of the core elements is the concept of "gacha" or probabilistic purchase, where instead of selling an item for a price, they sell a low probability of getting what you actually want for a lower price... but in the end people try over and over again and easily lose track of their purchases and end up spending more.
Some forms of gacha are no longer legal (e.g: kompu gacha), due to their exceptional ability to make people spend... last time I checked the thing was "box gacha".
Another way of making revenue is through "events", which are competitions, but their outcome is heavily influenced by how much you spend. They're basically auctions.
The thing is... in the end people don't really win. To win an event in a top grossing game you might need probably a thousand dollars. It's not worth it.