In practice people use the blockchain to move assets between accounts tied to some of the many competing centralized trading markets (of which Binance is only t

In practice people use the blockchain to move assets between accounts tied to some of the many competing centralized trading markets (of which Binance is only the biggest one). They also use it for OTC transactions, which are typically also hedged on centralized markets due to their uncertainty. The centralized markets also function as banks, where you can borrow or cross-margin your positions. So it works, it's just that only using blockchain is not good enough to deal with speculation needs and market volatility.