They're loans so where do they get the income to pay off the interest? If I attempt something like this via Interactive Brokers (which generally has the best rates), it would cost me 5-6%: https://www.interactivebrokers.com/en/trading/margin-rates.p... I'd figure if you're a billionaire, with multi-millions in collateral, the rate is probably significantly lower, but they still need to pay down the interest.
IBKR is charging Fed Funds rate + 0.5% at >$200k.
Why would they ever offer anyone significantly less than that rewardless if they are billionaires or not? They be losing money on those loans..