Banks, casinos, and exchanges on how they handle bank runs

Banks make money from interest rate spreads, but their cash reserves are insufficient—so they fear a bank run.
Casinos are games of probability bias; as long as they don't get caught cheating, they won't lose money in the long run, so their cash reserves are definitely enough—casinos don't fear bank runs, they fear being accused of unfairness.
Exchanges are fee-based businesses that hold funds in custody; as long as they don't engage in betting themselves, they are unlikely to lose money. As long as they don't misuse assets, they won't go bankrupt—if an exchange doesn't bet itself, it doesn't fear a bank run. It fears public opinion and fears you withdrawing liquidity.