I have a question.....❓

Regarding ( Spot trading ) 🖊️
can anyone answer 🤌

when we buy a coin, it stays in the holding, and at the same time when we place an order to sell, it appears in the open order,

when the coin is sell,
its quantity ends with the open order.

👉 : But why doesn't the quantity in the holding End itself ....?❓