before crypto there was a market phenomenon that I personally have no knowledge of but an acquaintance at a big bank which facilitated a lot of FX trading was very happy at one point that he was sent to Japan, where retail FX trading had become a huge fad, like crypto now. He was a prop trader for the bank and made a lot of his money going against retail traders. Presumably it was exploiting information asymmetries, partly, but probably also just simply harvesting fees and spreads.

everything old is new again