It’s not for expenses, it because stocks don’t actually settle (i.e. exchange cash for shares) until a few days later. But Robinhood lets customer trade again i

It’s not for expenses, it because stocks don’t actually settle (i.e. exchange cash for shares) until a few days later. But Robinhood lets customer trade again immediately. They are financing this turnover. When volumes go huge and turnover increases, they have a lot more capital tied up in this process.