Why Discount Account in Vendor Bills is prompting to select an Expense Account instead of an Income Account?

Why Discount Account in Vendor Bills is prompting to select an Expense Account instead of an Income Account?

In case of Vendor Bills, the discount ledger should be of Income Type account as because this discount is a purchase discount that will be received by the buyers. In other words, this should be treated as 'Discount Received' which I believe is supposed to be an Income rather than Expense.

Please help