The margin ratio of an exchange is different from that of a futures company, and it will generally increase by several percentage points. For example, the exchange needs 10%, and the futures company needs 20%. When you trade, half of the funds will be kept by the futures company. This part of the funds actually exists in the account opened by the futures company in the bank, and the bank will of course pay interest to the futures company. This is on the one hand, as long as the overall position changes little, the amount stability is high.
The other part is that after you deposit money, your money has actually reached the account opened by the futures company in the bank, and the bank also needs to pay interest to the futures company, but because you can withdraw money at any time, the amount stability is low.
Comparatively speaking, the handling fee is an important source of income.