Easy. As an exchange almost all your volume is “off chain” transactions between two traders. And since you aren’t audited or beholden to any financial regulat

Easy. As an exchange almost all your volume is “off chain” transactions between two traders. And since you aren’t audited or beholden to any financial regulation there is nothing stopping you from having one side of the trade be your own bot. All that bot does is sell newly created fake bitcoin and keeps the dirty USD fiat for the exchange owner. Again since the system isn’t audited, the exchange can have massively more “bitcoin” in its database than it actually has on the blockchain. The system (Er, scam) can work just fine until a bunch of folks start withdrawing bitcoin. Since virtually all of the exchanges are unaudited, sketchy “businesses” I wouldn’t be surprised if they all run this way. It might come to pass the almost all of the exchange volume consists of trading fake bitcoin that is backed by almost no real bitcoin.